diff --git a/core/class/sleekDB/Cache.php b/core/class/sleekDB/Cache.php
new file mode 100644
index 00000000..806cb2a9
--- /dev/null
+++ b/core/class/sleekDB/Cache.php
@@ -0,0 +1,309 @@
+<?php
+
+namespace SleekDB;
+
+use Closure;
+use Exception;
+use ReflectionFunction;
+use SleekDB\Classes\IoHelper;
+use SleekDB\Exceptions\IOException;
+
+/**
+ * Class Cache
+ * Caching layer of SleekDB, handles everything regarding caching.
+ */
+class Cache
+{
+
+  const DEFAULT_CACHE_DIR = "cache/";
+  const NO_LIFETIME_FILE_STRING = "no_lifetime";
+
+  /**
+   * Lifetime in seconds or deletion with deleteAll
+   * @var int|null
+   */
+  protected $lifetime;
+
+  protected $cachePath = "";
+
+  protected $cacheDir = "";
+
+  protected $tokenArray;
+
+  /**
+   * Cache constructor.
+   * @param string $storePath
+   * @param array $cacheTokenArray
+   * @param int|null $cacheLifetime
+   */
+  public function __construct(string $storePath, array &$cacheTokenArray, $cacheLifetime)
+  {
+    // TODO make it possible to define custom cache directory.
+//    $cacheDir = "";
+//    $this->setCacheDir($cacheDir);
+
+    $this->setCachePath($storePath);
+
+    $this->setTokenArray($cacheTokenArray);
+
+    $this->lifetime = $cacheLifetime;
+  }
+
+  /**
+   * Retrieve the cache lifetime for current query.
+   * @return int|null lifetime in seconds (int) or no lifetime with null
+   */
+  public function getLifetime()
+  {
+    return $this->lifetime;
+  }
+
+  /**
+   * Retrieve the path to cache folder of current store.
+   * @return string path to cache directory
+   */
+  public function getCachePath(): string
+  {
+    return $this->cachePath;
+  }
+
+  /**
+   * Retrieve the cache token used as filename to store cache file.
+   * @return string unique token for current query.
+   */
+  public function getToken(): string
+  {
+    $tokenArray = $this->getTokenArray();
+    $tokenArray = self::convertClosuresToString($tokenArray);
+
+    return md5(json_encode($tokenArray));
+  }
+
+  /**
+   * Delete all cache files for current store.
+   * @return bool
+   */
+  public function deleteAll(): bool
+  {
+    return IoHelper::deleteFiles(glob($this->getCachePath()."*"));
+  }
+
+  /**
+   * Delete all cache files with no lifetime (null) in current store.
+   * @return bool
+   */
+  public function deleteAllWithNoLifetime(): bool
+  {
+    $noLifetimeFileString = self::NO_LIFETIME_FILE_STRING;
+    return IoHelper::deleteFiles(glob($this->getCachePath()."*.$noLifetimeFileString.json"));
+  }
+
+  /**
+   * Save content for current query as a cache file.
+   * @param array $content
+   * @throws IOException if cache folder is not writable or saving failed.
+   */
+  public function set(array $content){
+    $lifetime = $this->getLifetime();
+    $cachePath = $this->getCachePath();
+    $token = $this->getToken();
+
+    $noLifetimeFileString = self::NO_LIFETIME_FILE_STRING;
+    $cacheFile = $cachePath . $token . ".$noLifetimeFileString.json";
+
+    if(is_int($lifetime)){
+      $cacheFile = $cachePath . $token . ".$lifetime.json";
+    }
+
+    IoHelper::writeContentToFile($cacheFile, json_encode($content));
+  }
+
+  /**
+   * Retrieve content of cache file.
+   * @return array|null array on success, else null
+   * @throws IOException if cache file is not readable or does not exist.
+   */
+  public function get(){
+    $cachePath = $this->getCachePath();
+    $token = $this->getToken();
+
+    $cacheFile = null;
+
+    IoHelper::checkRead($cachePath);
+
+    $cacheFiles = glob($cachePath.$token."*.json");
+
+    if($cacheFiles !== false && count($cacheFiles) > 0){
+      $cacheFile = $cacheFiles[0];
+    }
+
+    if(!empty($cacheFile)){
+      $cacheParts = explode(".", $cacheFile);
+      if(count($cacheParts) >= 3){
+        $lifetime = $cacheParts[count($cacheParts) - 2];
+        if(is_numeric($lifetime)){
+          if($lifetime === "0"){
+            return json_decode(IoHelper::getFileContent($cacheFile), true);
+          }
+          $fileExpiredAfter = filemtime($cacheFile) + (int) $lifetime;
+          if(time() <= $fileExpiredAfter){
+            return json_decode(IoHelper::getFileContent($cacheFile), true);
+          }
+          IoHelper::deleteFile($cacheFile);
+        } else if($lifetime === self::NO_LIFETIME_FILE_STRING){
+            return json_decode(IoHelper::getFileContent($cacheFile), true);
+        }
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Delete cache file/s for current query.
+   * @return bool
+   */
+  public function delete(): bool
+  {
+    return IoHelper::deleteFiles(glob($this->getCachePath().$this->getToken()."*.json"));
+  }
+
+  /**
+   * @param string $storePath
+   * @return Cache
+   */
+  private function setCachePath(string $storePath): Cache
+  {
+    $cachePath = "";
+    $cacheDir = $this->getCacheDir();
+
+    if(!empty($storePath)){
+      IoHelper::normalizeDirectory($storePath);
+      $cachePath = $storePath . $cacheDir;
+    }
+
+    $this->cachePath = $cachePath;
+
+    return $this;
+  }
+
+  /**
+   * Set the cache token array used for cache token string generation.
+   * @param array $tokenArray
+   * @return Cache
+   */
+  private function setTokenArray(array &$tokenArray): Cache
+  {
+    $this->tokenArray = &$tokenArray;
+    return $this;
+  }
+
+  /**
+   * Retrieve the cache token array.
+   * @return array
+   */
+  private function getTokenArray(): array
+  {
+    return $this->tokenArray;
+  }
+
+  /**
+   * Convert one or multiple closures to string. If array provided, recursively.
+   * @param mixed $data
+   * @return mixed
+   */
+  private static function convertClosuresToString($data){
+    if(!is_array($data)){
+      if($data instanceof \Closure){
+        return self::getClosureAsString($data);
+      }
+      return $data;
+    }
+    foreach ($data as $key => $token){
+      if(is_array($token)){
+        $data[$key] = self::convertClosuresToString($token);
+      } else if($token instanceof \Closure){
+        $data[$key] = self::getClosureAsString($token);
+      }
+    }
+    return $data;
+  }
+
+  /**
+   * Retrieve a string representation of a closure that can be used to differentiate between closures
+   * when generating the cache token string.
+   * @param Closure $closure
+   * @return false|string string representation of closure or false on failure.
+   */
+  private static function getClosureAsString(Closure $closure)
+  {
+    try{
+      $reflectionFunction = new ReflectionFunction($closure); // get reflection object
+    } catch (Exception $exception){
+      return false;
+    }
+    $filePath = $reflectionFunction->getFileName();  // absolute path of php file containing function
+    $startLine = $reflectionFunction->getStartLine(); // start line of function
+    $endLine = $reflectionFunction->getEndLine(); // end line of function
+    $lineSeparator = PHP_EOL; // line separator "\n"
+
+    $staticVariables = $reflectionFunction->getStaticVariables();
+    $staticVariables = var_export($staticVariables, true);
+
+    if($filePath === false || $startLine === false || $endLine === false){
+      return false;
+    }
+
+    $startEndDifference = $endLine - $startLine;
+
+    $startLine--; // -1 to use it with the array representation of the file
+
+    if($startLine < 0 || $startEndDifference < 0){
+      return false;
+    }
+
+    // get content of file containing function
+    $fp = fopen($filePath, 'rb');
+    $fileContent = "";
+    if(flock($fp, LOCK_SH)){
+      $fileContent = @stream_get_contents($fp);
+    }
+    flock($fp, LOCK_UN);
+    fclose($fp);
+
+    if(empty($fileContent)){
+      return false;
+    }
+
+    // separate the file into an array containing every line as one element
+    $fileContentArray = explode($lineSeparator, $fileContent);
+    if(count($fileContentArray) < $endLine){
+      return false;
+    }
+
+    // return the part of the file containing the function as a string.
+    $functionString = implode("", array_slice($fileContentArray, $startLine, $startEndDifference + 1));
+    $functionString .= "|staticScopeVariables:".$staticVariables;
+    return $functionString;
+  }
+
+  /**
+   * Set the cache directory name.
+   * @param string $cacheDir
+   * @return Cache
+   */
+  private function setCacheDir(string $cacheDir): Cache
+  {
+    IoHelper::normalizeDirectory($cacheDir);
+    $this->cacheDir = $cacheDir;
+    return $this;
+  }
+
+  /**
+   * Retrieve the cache directory name or the default cache directory name if empty.
+   * @return string
+   */
+  private function getCacheDir(): string
+  {
+    return (!empty($this->cacheDir)) ? $this->cacheDir : self::DEFAULT_CACHE_DIR;
+  }
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/CacheHandler.php b/core/class/sleekDB/Classes/CacheHandler.php
new file mode 100644
index 00000000..2104d9f8
--- /dev/null
+++ b/core/class/sleekDB/Classes/CacheHandler.php
@@ -0,0 +1,129 @@
+<?php
+
+
+namespace SleekDB\Classes;
+
+
+use SleekDB\Cache;
+use SleekDB\Exceptions\IOException;
+use SleekDB\QueryBuilder;
+
+/**
+ * Class CacheHandler
+ * Bridge between Query and Cache
+ */
+class CacheHandler
+{
+  /**
+   * @var Cache
+   */
+  protected $cache;
+
+  protected $cacheTokenArray;
+  protected $regenerateCache;
+  protected $useCache;
+
+  /**
+   * CacheHandler constructor.
+   * @param string $storePath
+   * @param QueryBuilder $queryBuilder
+   */
+  public function __construct(string $storePath, QueryBuilder $queryBuilder)
+  {
+    $this->cacheTokenArray = $queryBuilder->_getCacheTokenArray();
+
+    $queryBuilderProperties = $queryBuilder->_getConditionProperties();
+    $this->useCache = $queryBuilderProperties["useCache"];
+    $this->regenerateCache = $queryBuilderProperties["regenerateCache"];
+
+    $this->cache = new Cache($storePath, $this->_getCacheTokenArray(), $queryBuilderProperties["cacheLifetime"]);
+  }
+
+  /**
+   * @return Cache
+   */
+  public function getCache(): Cache
+  {
+    return $this->cache;
+  }
+
+  /**
+   * Get results from cache
+   * @return array|null
+   * @throws IOException
+   */
+  public function getCacheContent($getOneDocument)
+  {
+    if($this->getUseCache() !== true){
+      return null;
+    }
+
+    $this->updateCacheTokenArray(['oneDocument' => $getOneDocument]);
+
+    if($this->regenerateCache === true) {
+      $this->getCache()->delete();
+    }
+
+    $cacheResults = $this->getCache()->get();
+    if(is_array($cacheResults)) {
+      return $cacheResults;
+    }
+
+    return null;
+  }
+
+  /**
+   * Add content to cache
+   * @param array $results
+   * @throws IOException
+   */
+  public function setCacheContent(array $results)
+  {
+    if($this->getUseCache() === true){
+      $this->getCache()->set($results);
+    }
+  }
+
+  /**
+   * Delete all cache files that have no lifetime.
+   * @return bool
+   */
+  public function deleteAllWithNoLifetime(): bool
+  {
+    return $this->getCache()->deleteAllWithNoLifetime();
+  }
+
+  /**
+   * Returns a reference to the array used for cache token generation
+   * @return array
+   */
+  public function &_getCacheTokenArray(): array
+  {
+    return $this->cacheTokenArray;
+  }
+
+  /**
+   * @param array $tokenUpdate
+   */
+  private function updateCacheTokenArray(array $tokenUpdate)
+  {
+    if(empty($tokenUpdate)) {
+      return;
+    }
+    $cacheTokenArray = $this->_getCacheTokenArray();
+    foreach ($tokenUpdate as $key => $value){
+      $cacheTokenArray[$key] = $value;
+    }
+    $this->cacheTokenArray = $cacheTokenArray;
+  }
+
+  /**
+   * Status if cache is used or not
+   * @return bool
+   */
+  private function getUseCache(): bool
+  {
+    return $this->useCache;
+  }
+
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/ConditionsHandler.php b/core/class/sleekDB/Classes/ConditionsHandler.php
new file mode 100644
index 00000000..0bb59de6
--- /dev/null
+++ b/core/class/sleekDB/Classes/ConditionsHandler.php
@@ -0,0 +1,433 @@
+<?php
+
+
+namespace SleekDB\Classes;
+
+
+use SleekDB\Exceptions\InvalidArgumentException;
+use DateTime;
+use Exception;
+use Throwable;
+
+/**
+ * Class ConditionsHandler
+ * Handle all types of conditions to check if a document has passed.
+ */
+class ConditionsHandler
+{
+
+  /**
+   * Get the result of an condition.
+   * @param string $condition
+   * @param mixed $fieldValue value of current field
+   * @param mixed $value value to check
+   * @return bool
+   * @throws InvalidArgumentException
+   */
+  public static function verifyCondition(string $condition, $fieldValue, $value): bool
+  {
+
+    if($value instanceof DateTime){
+      // compare timestamps
+
+      // null, false or an empty string will convert to current date and time.
+      // That is not what we want.
+      if(empty($fieldValue)){
+        return false;
+      }
+      $value = $value->getTimestamp();
+      $fieldValue = self::convertValueToTimeStamp($fieldValue);
+    }
+
+    $condition = strtolower(trim($condition));
+    switch ($condition){
+      case "=":
+      case "===":
+        return ($fieldValue === $value);
+      case "==":
+        return ($fieldValue == $value);
+      case "<>":
+        return ($fieldValue != $value);
+      case "!==":
+      case "!=":
+        return ($fieldValue !== $value);
+      case ">":
+        return ($fieldValue > $value);
+      case ">=":
+        return ($fieldValue >= $value);
+      case "<":
+        return ($fieldValue < $value);
+      case "<=":
+        return ($fieldValue <= $value);
+      case "not like":
+      case "like":
+
+        if(!is_string($value)){
+          throw new InvalidArgumentException("When using \"LIKE\" or \"NOT LIKE\" the value has to be a string.");
+        }
+
+        // escape characters that are part of regular expression syntax
+        // https://www.php.net/manual/en/function.preg-quote.php
+        // We can not use preg_quote because the following characters are also wildcard characters in sql
+        // so we will not escape them: [ ^ ] -
+        $charactersToEscape = [".", "\\", "+", "*", "?", "$", "(", ")", "{", "}", "=", "!", "<", ">", "|", ":",  "#"];
+        foreach ($charactersToEscape as $characterToEscape){
+          $value = str_replace($characterToEscape, "\\".$characterToEscape, $value);
+        }
+
+        $value = str_replace(array('%', '_'), array('.*', '.{1}'), $value); // (zero or more characters) and (single character)
+        $pattern = "/^" . $value . "$/i";
+        $result = (preg_match($pattern, $fieldValue) === 1);
+        return ($condition === "not like") ? !$result : $result;
+
+      case "not in":
+      case "in":
+        if(!is_array($value)){
+          $value = (!is_object($value) && !is_array($value) && !is_null($value)) ? $value : gettype($value);
+          throw new InvalidArgumentException("When using \"in\" and \"not in\" you have to check against an array. Got: $value");
+        }
+        if(!empty($value)){
+          (list($firstElement) = $value);
+          if($firstElement instanceof DateTime){
+            // if the user wants to use DateTime, every element of the array has to be an DateTime object.
+
+            // compare timestamps
+
+            // null, false or an empty string will convert to current date and time.
+            // That is not what we want.
+            if(empty($fieldValue)){
+              return false;
+            }
+
+            foreach ($value as $key => $item){
+              if(!($item instanceof DateTime)){
+                throw new InvalidArgumentException("If one DateTime object is given in an \"IN\" or \"NOT IN\" comparison, every element has to be a DateTime object!");
+              }
+              $value[$key] = $item->getTimestamp();
+            }
+
+            $fieldValue = self::convertValueToTimeStamp($fieldValue);
+          }
+        }
+        $result = in_array($fieldValue, $value, true);
+        return ($condition === "not in") ? !$result : $result;
+      case "not between":
+      case "between":
+
+        if(!is_array($value) || ($valueLength = count($value)) !== 2){
+          $value = (!is_object($value) && !is_array($value) && !is_null($value)) ? $value : gettype($value);
+          if(isset($valueLength)){
+            $value .= " | Length: $valueLength";
+          }
+          throw new InvalidArgumentException("When using \"between\" you have to check against an array with a length of 2. Got: $value");
+        }
+
+        list($startValue, $endValue) = $value;
+
+        $result = (
+          self::verifyCondition(">=", $fieldValue, $startValue)
+          && self::verifyCondition("<=", $fieldValue, $endValue)
+        );
+
+        return ($condition === "not between") ? !$result : $result;
+      case "not contains":
+      case "contains":
+
+        if(!is_array($fieldValue)){
+          return ($condition === "not contains");
+        }
+
+        $fieldValues = [];
+
+        if($value instanceof DateTime){
+          // compare timestamps
+          $value = $value->getTimestamp();
+
+          foreach ($fieldValue as $item){
+            // null, false or an empty string will convert to current date and time.
+            // That is not what we want.
+            if(empty($item)){
+              continue;
+            }
+            try{
+              $fieldValues[] = self::convertValueToTimeStamp($item);
+            } catch (Exception $exception){
+            }
+          }
+        }
+
+        if(!empty($fieldValues)){
+          $result = in_array($value, $fieldValues, true);
+        } else {
+          $result = in_array($value, $fieldValue, true);
+        }
+
+        return ($condition === "not contains") ? !$result : $result;
+      case 'exists':
+        return $fieldValue === $value;
+      default:
+        throw new InvalidArgumentException("Condition \"$condition\" is not allowed.");
+    }
+  }
+
+  /**
+   * @param array $element condition or operation
+   * @param array $data
+   * @return bool
+   * @throws InvalidArgumentException
+   */
+  public static function handleWhereConditions(array $element, array $data): bool
+  {
+    if(empty($element)){
+      throw new InvalidArgumentException("Malformed where statement! Where statements can not contain empty arrays.");
+    }
+    if(array_keys($element) !== range(0, (count($element) - 1))){
+      throw new InvalidArgumentException("Malformed where statement! Associative arrays are not allowed.");
+    }
+    // element is a where condition
+    if(is_string($element[0]) && is_string($element[1])){
+      if(count($element) !== 3){
+        throw new InvalidArgumentException("Where conditions have to be [fieldName, condition, value]");
+      }
+
+      $fieldName = $element[0];
+      $condition = strtolower(trim($element[1]));
+      $fieldValue = ($condition === 'exists')
+        ? NestedHelper::nestedFieldExists($fieldName, $data)
+        : NestedHelper::getNestedValue($fieldName, $data);
+
+      return self::verifyCondition($condition, $fieldValue, $element[2]);
+    }
+
+    // element is an array "brackets"
+
+    // prepare results array - example: [true, "and", false]
+    $results = [];
+    foreach ($element as $value){
+      if(is_array($value)){
+        $results[] = self::handleWhereConditions($value, $data);
+      } else if (is_string($value)) {
+        $results[] = $value;
+      } else if($value instanceof \Closure){
+        $result = $value($data);
+        if(!is_bool($result)){
+          $resultType = gettype($result);
+          $errorMsg = "The closure in the where condition needs to return a boolean. Got: $resultType";
+          throw new InvalidArgumentException($errorMsg);
+        }
+        $results[] = $result;
+      } else {
+        $value = (!is_object($value) && !is_array($value) && !is_null($value)) ? $value : gettype($value);
+        throw new InvalidArgumentException("Invalid nested where statement element! Expected condition or operation, got: \"$value\"");
+      }
+    }
+
+    // first result as default value
+    $returnValue = array_shift($results);
+
+    if(is_bool($returnValue) === false){
+      throw new InvalidArgumentException("Malformed where statement! First part of the statement have to be a condition.");
+    }
+
+    // used to prioritize the "and" operation.
+    $orResults = [];
+
+    // use results array to get the return value of the conditions within the bracket
+    while(!empty($results) || !empty($orResults)){
+
+      if(empty($results)) {
+        if($returnValue === true){
+          // we need to check anymore, because the result of true || false is true
+          break;
+        }
+        // $orResults is not empty.
+        $nextResult = array_shift($orResults);
+        $returnValue = $returnValue || $nextResult;
+        continue;
+      }
+
+      $operationOrNextResult = array_shift($results);
+
+      if(is_string($operationOrNextResult)){
+        $operation = $operationOrNextResult;
+
+        if(empty($results)){
+          throw new InvalidArgumentException("Malformed where statement! Last part of a condition can not be a operation.");
+        }
+        $nextResult = array_shift($results);
+
+        if(!is_bool($nextResult)){
+          throw new InvalidArgumentException("Malformed where statement! Two operations in a row are not allowed.");
+        }
+      } else if(is_bool($operationOrNextResult)){
+        $operation = "AND";
+        $nextResult = $operationOrNextResult;
+      } else {
+        throw new InvalidArgumentException("Malformed where statement! A where statement have to contain just operations and conditions.");
+      }
+
+      if(!in_array(strtolower($operation), ["and", "or"])){
+        $operation = (!is_object($operation) && !is_array($operation) && !is_null($operation)) ? $operation : gettype($operation);
+        throw new InvalidArgumentException("Expected 'and' or 'or' operator got \"$operation\"");
+      }
+
+      // prepare $orResults execute after all "and" are done.
+      if(strtolower($operation) === "or"){
+        $orResults[] = $returnValue;
+        $returnValue = $nextResult;
+        continue;
+      }
+
+      $returnValue = $returnValue && $nextResult;
+
+    }
+
+    return $returnValue;
+  }
+
+  /**
+   * @param array $results
+   * @param array $currentDocument
+   * @param array $distinctFields
+   * @return bool
+   */
+  public static function handleDistinct(array $results, array $currentDocument, array $distinctFields): bool
+  {
+    // Distinct data check.
+    foreach ($results as $result) {
+      foreach ($distinctFields as $field) {
+        try {
+          $storePassed = (NestedHelper::getNestedValue($field, $result) !== NestedHelper::getNestedValue($field, $currentDocument));
+        } catch (Throwable $th) {
+          continue;
+        }
+        if ($storePassed === false) {
+          return false;
+        }
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * @param array $data
+   * @param bool $storePassed
+   * @param array $nestedWhereConditions
+   * @return bool
+   * @throws InvalidArgumentException
+   * @deprecated since version 2.3, use handleWhereConditions instead.
+   */
+  public static function handleNestedWhere(array $data, bool $storePassed, array $nestedWhereConditions): bool
+  {
+    // TODO remove nested where with v3.0
+
+    if(empty($nestedWhereConditions)){
+      return $storePassed;
+    }
+
+    // the outermost operation specify how the given conditions are connected with other conditions,
+    // like the ones that are specified using the where, orWhere, in or notIn methods
+    $outerMostOperation = (array_keys($nestedWhereConditions))[0];
+    $nestedConditions = $nestedWhereConditions[$outerMostOperation];
+
+    // specifying outermost is optional and defaults to "and"
+    $outerMostOperation = (is_string($outerMostOperation)) ? strtolower($outerMostOperation) : "and";
+
+    // if the document already passed the store with another condition, we dont need to check it.
+    if($outerMostOperation === "or" && $storePassed === true){
+      return true;
+    }
+
+    return self::_nestedWhereHelper($nestedConditions, $data);
+  }
+
+  /**
+   * @param array $element
+   * @param array $data
+   * @return bool
+   * @throws InvalidArgumentException
+   * @deprecated since version 2.3. use _handleWhere instead
+   */
+  private static function _nestedWhereHelper(array $element, array $data): bool
+  {
+    // TODO remove nested where with v3.0
+    // element is a where condition
+    if(array_keys($element) === range(0, (count($element) - 1)) && is_string($element[0])){
+      if(count($element) !== 3){
+        throw new InvalidArgumentException("Where conditions have to be [fieldName, condition, value]");
+      }
+
+      $fieldValue = NestedHelper::getNestedValue($element[0], $data);
+
+      return self::verifyCondition($element[1], $fieldValue, $element[2]);
+    }
+
+    // element is an array "brackets"
+
+    // prepare results array - example: [true, "and", false]
+    $results = [];
+    foreach ($element as $value){
+      if(is_array($value)){
+        $results[] = self::_nestedWhereHelper($value, $data);
+      } else if (is_string($value)){
+        $results[] = $value;
+      } else {
+        $value = (!is_object($value) && !is_array($value)) ? $value : gettype($value);
+        throw new InvalidArgumentException("Invalid nested where statement element! Expected condition or operation, got: \"$value\"");
+      }
+    }
+
+    if(count($results) < 3){
+      throw new InvalidArgumentException("Malformed nested where statement! A condition consists of at least 3 elements.");
+    }
+
+    // first result as default value
+    $returnValue = array_shift($results);
+
+    // use results array to get the return value of the conditions within the bracket
+    while(!empty($results)){
+      $operation = array_shift($results);
+      $nextResult = array_shift($results);
+
+      if(((count($results) % 2) !== 0)){
+        throw new InvalidArgumentException("Malformed nested where statement!");
+      }
+
+      if(!is_string($operation) || !in_array(strtolower($operation), ["and", "or"])){
+        $operation = (!is_object($operation) && !is_array($operation)) ? $operation : gettype($operation);
+        throw new InvalidArgumentException("Expected 'and' or 'or' operator got \"$operation\"");
+      }
+
+      if(strtolower($operation) === "and"){
+        $returnValue = $returnValue && $nextResult;
+      } else {
+        $returnValue = $returnValue || $nextResult;
+      }
+    }
+
+    return $returnValue;
+  }
+
+  /**
+   * @param $value
+   * @return int
+   * @throws InvalidArgumentException
+   */
+  private static function convertValueToTimeStamp($value): int
+  {
+    $value = (is_string($value)) ? trim($value) : $value;
+    try{
+      return (new DateTime($value))->getTimestamp();
+    } catch (Exception $exception){
+      $value = (!is_object($value) && !is_array($value))
+        ? $value
+        : gettype($value);
+      throw new InvalidArgumentException(
+        "DateTime object given as value to check against. "
+        . "Could not convert value into DateTime. "
+        . "Value: $value"
+      );
+    }
+  }
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/DocumentFinder.php b/core/class/sleekDB/Classes/DocumentFinder.php
new file mode 100644
index 00000000..d2014966
--- /dev/null
+++ b/core/class/sleekDB/Classes/DocumentFinder.php
@@ -0,0 +1,387 @@
+<?php
+
+
+namespace SleekDB\Classes;
+
+
+use Exception;
+use SleekDB\Exceptions\InvalidArgumentException;
+use SleekDB\Exceptions\IOException;
+use SleekDB\Query;
+use SleekDB\Store;
+
+/**
+ * Class DocumentFinder
+ * Find documents
+ */
+class DocumentFinder
+{
+  protected $storePath;
+  protected $queryBuilderProperties;
+  protected $primaryKey;
+
+  public function __construct(string $storePath, array $queryBuilderProperties, string $primaryKey)
+  {
+    $this->storePath = $storePath;
+    $this->queryBuilderProperties = $queryBuilderProperties;
+    $this->primaryKey = $primaryKey;
+  }
+
+  /**
+   * @param bool $getOneDocument
+   * @param bool $reduceAndJoinPossible
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findDocuments(bool $getOneDocument, bool $reduceAndJoinPossible): array
+  {
+    $queryBuilderProperties = $this->queryBuilderProperties;
+    $dataPath = $this->getDataPath();
+    $primaryKey = $this->primaryKey;
+
+    $found = [];
+    // Start collecting and filtering data.
+    IoHelper::checkRead($dataPath);
+
+    $conditions = $queryBuilderProperties["whereConditions"];
+    $distinctFields = $queryBuilderProperties["distinctFields"];
+    $nestedWhereConditions = $queryBuilderProperties["nestedWhere"];
+    $listOfJoins = $queryBuilderProperties["listOfJoins"];
+    $search = $queryBuilderProperties["search"];
+    $searchOptions = $queryBuilderProperties["searchOptions"];
+    $groupBy = $queryBuilderProperties["groupBy"];
+    $havingConditions = $queryBuilderProperties["havingConditions"];
+    $fieldsToSelect = $queryBuilderProperties["fieldsToSelect"];
+    $orderBy = $queryBuilderProperties["orderBy"];
+    $skip = $queryBuilderProperties["skip"];
+    $limit = $queryBuilderProperties["limit"];
+    $fieldsToExclude = $queryBuilderProperties["fieldsToExclude"];
+
+    unset($queryBuilderProperties);
+
+    if ($handle = opendir($dataPath)) {
+
+      while (false !== ($entry = readdir($handle))) {
+
+        if ($entry === "." || $entry === "..") {
+          continue;
+        }
+
+        $documentPath = $dataPath . $entry;
+
+        try{
+          $data = IoHelper::getFileContent($documentPath);
+        } catch (Exception $exception){
+          continue;
+        }
+        $data = @json_decode($data, true);
+        if (!is_array($data)) {
+          continue;
+        }
+
+        $storePassed = true;
+
+        // Append only passed data from this store.
+
+        // Process conditions
+        if(!empty($conditions)) {
+          // Iterate each conditions.
+          $storePassed = ConditionsHandler::handleWhereConditions($conditions, $data);
+        }
+
+        // TODO remove nested where with version 3.0
+        $storePassed = ConditionsHandler::handleNestedWhere($data, $storePassed, $nestedWhereConditions);
+
+        if ($storePassed === true && count($distinctFields) > 0) {
+          $storePassed = ConditionsHandler::handleDistinct($found, $data, $distinctFields);
+        }
+
+        if ($storePassed === true) {
+          $found[] = $data;
+
+          // if we just check for existence or want to return the first item, we dont need to look for more documents
+          if ($getOneDocument === true) {
+            break;
+          }
+        }
+      }
+      closedir($handle);
+    }
+
+    // apply additional changes to result like sort and limit
+
+    if($reduceAndJoinPossible === true){
+      DocumentReducer::joinData($found, $listOfJoins);
+    }
+
+    if (count($found) > 0) {
+      self::performSearch($found, $search, $searchOptions);
+    }
+
+    if ($reduceAndJoinPossible === true && !empty($groupBy) && count($found) > 0) {
+
+      DocumentReducer::handleGroupBy(
+        $found,
+        $groupBy,
+        $fieldsToSelect
+      );
+    }
+
+    if($reduceAndJoinPossible === true && empty($groupBy) && count($found) > 0){
+      // select specific fields
+      DocumentReducer::selectFields($found, $primaryKey, $fieldsToSelect);
+    }
+
+    if(count($found) > 0){
+      self::handleHaving($found, $havingConditions);
+    }
+
+    if($reduceAndJoinPossible === true && count($found) > 0){
+      // exclude specific fields
+      DocumentReducer::excludeFields($found, $fieldsToExclude);
+    }
+
+    if(count($found) > 0){
+      // sort the data.
+      self::sort($found, $orderBy);
+    }
+
+
+    if(count($found) > 0) {
+      // Skip data
+      self::skip($found, $skip);
+    }
+
+    if(count($found) > 0) {
+      // Limit data.
+      self::limit($found, $limit);
+    }
+
+    return $found;
+  }
+
+  /**
+   * @return string
+   */
+  private function getDataPath(): string
+  {
+    return $this->storePath . Store::dataDirectory;
+  }
+
+  /**
+   * @param array $found
+   * @param array $orderBy
+   * @throws InvalidArgumentException
+   */
+  private static function sort(array &$found, array $orderBy){
+    if (!empty($orderBy)) {
+
+      $resultSortArray = [];
+
+      foreach ($orderBy as $orderByClause){
+        // Start sorting on all data.
+        $order = $orderByClause['order'];
+        $fieldName = $orderByClause['fieldName'];
+
+        $arrayColumn = [];
+        // Get value of the target field.
+        foreach ($found as $value) {
+          $arrayColumn[] = NestedHelper::getNestedValue($fieldName, $value);
+        }
+
+        $resultSortArray[] = $arrayColumn;
+
+        // Decide the order direction.
+        // order will be asc or desc (check is done in QueryBuilder class)
+        $resultSortArray[] = ($order === 'asc') ? SORT_ASC : SORT_DESC;
+
+      }
+
+      if(!empty($resultSortArray)){
+        $resultSortArray[] = &$found;
+        array_multisort(...$resultSortArray);
+      }
+      unset($resultSortArray);
+    }
+  }
+
+  /**
+   * @param array $found
+   * @param $skip
+   */
+  private static function skip(array &$found, $skip){
+    if (empty($skip) || $skip <= 0) {
+      return;
+    }
+    $found = array_slice($found, $skip);
+  }
+
+  /**
+   * @param array $found
+   * @param $limit
+   */
+  private static function limit(array &$found, $limit){
+    if (empty($limit) || $limit <= 0) {
+      return;
+    }
+    $found = array_slice($found, 0, $limit);
+  }
+
+  /**
+   * Do a search in store objects. This is like a doing a full-text search.
+   * @param array $found
+   * @param array $search
+   * @param array $searchOptions
+   * @throws InvalidArgumentException
+   */
+  private static function performSearch(array &$found, array $search, array $searchOptions)
+  {
+    if(empty($search)){
+      return;
+    }
+    $minLength = $searchOptions["minLength"];
+    $searchScoreKey = $searchOptions["scoreKey"];
+    $searchMode = $searchOptions["mode"];
+    $searchAlgorithm = $searchOptions["algorithm"];
+
+    $scoreMultiplier = 64;
+    $encoding = "UTF-8";
+
+    $fields = $search["fields"];
+    $query = $search["query"];
+    $lowerQuery = mb_strtolower($query, $encoding);
+    $exactQuery  = preg_quote($query, "/");
+
+    $fieldsLength = count($fields);
+
+    $highestScore = $scoreMultiplier ** $fieldsLength;
+
+    // split query
+    $searchWords = preg_replace('/(\s)/u', ',', $query);
+    $searchWords = explode(",", $searchWords);
+
+    $prioritizeAlgorithm = (in_array($searchAlgorithm, [
+      Query::SEARCH_ALGORITHM["prioritize"],
+      Query::SEARCH_ALGORITHM["prioritize_position"]
+    ], true));
+
+    $positionAlgorithm = ($searchAlgorithm === Query::SEARCH_ALGORITHM["prioritize_position"]);
+
+    // apply min word length
+    $temp = [];
+    foreach ($searchWords as $searchWord){
+      if(strlen($searchWord) >= $minLength){
+        $temp[] = $searchWord;
+      }
+    }
+    $searchWords = $temp;
+    unset($temp);
+    $searchWords = array_map(static function($value){
+      return preg_quote($value, "/");
+    }, $searchWords);
+
+    // apply mode
+    if($searchMode === "and"){
+      $preg = "";
+      foreach ($searchWords as $searchWord){
+        $preg .= "(?=.*".$searchWord.")";
+      }
+      $preg = '/^' . $preg . '.*/im';
+      $pregOr = '!(' . implode('|', $searchWords) . ')!i';
+    } else {
+      $preg = '!(' . implode('|', $searchWords) . ')!i';
+    }
+
+    // search
+    foreach ($found as $foundKey => &$document) {
+      $searchHits = 0;
+      $searchScore = 0;
+      foreach ($fields as $key => $field) {
+        if($prioritizeAlgorithm){
+          $score = $highestScore / ($scoreMultiplier ** $key);
+        } else {
+          $score = $scoreMultiplier;
+        }
+        $value = NestedHelper::getNestedValue($field, $document);
+
+        if (!is_string($value) || $value === "") {
+          continue;
+        }
+
+        $lowerValue = mb_strtolower($value, $encoding);
+
+        if ($lowerQuery === $lowerValue) {
+          // exact match
+          $searchHits++;
+          $searchScore += 16 * $score;
+        } elseif ($positionAlgorithm && mb_strpos($lowerValue, $lowerQuery, 0, $encoding) === 0) {
+          // exact beginning match
+          $searchHits++;
+          $searchScore += 8 * $score;
+        } elseif ($matches = preg_match_all('!' . $exactQuery . '!i', $value)) {
+          // exact query match
+          $searchHits += $matches;
+//          $searchScore += 2 * $score;
+          $searchScore += $matches * 2 * $score;
+          if($searchAlgorithm === Query::SEARCH_ALGORITHM["hits_prioritize"]){
+            $searchScore += $matches * ($fieldsLength - $key);
+          }
+        }
+
+        $matchesArray = [];
+
+        $matches = ($searchMode === "and") ? preg_match($preg, $value) : preg_match_all($preg, $value, $matchesArray, PREG_OFFSET_CAPTURE);
+
+        if ($matches) {
+          // any match
+          $searchHits += $matches;
+          $searchScore += $matches * $score;
+          if($searchAlgorithm === Query::SEARCH_ALGORITHM["hits_prioritize"]) {
+            $searchScore += $matches * ($fieldsLength - $key);
+          }
+          // because the "and" search algorithm at most finds one match we also use the amount of word occurrences
+          if($searchMode === "and" && isset($pregOr) && ($matches = preg_match_all($pregOr, $value, $matchesArray, PREG_OFFSET_CAPTURE))){
+            $searchHits += $matches;
+            $searchScore += $matches * $score;
+          }
+        }
+
+        // we apply a small very small number to the score to differentiate the distance from the beginning
+        if($positionAlgorithm && $matches && !empty($matchesArray)){
+          $hitPosition = $matchesArray[0][0][1];
+          if(!is_int($hitPosition) || !($hitPosition > 0)){
+            $hitPosition = 1;
+          }
+          $searchScore += ($score / $highestScore) * ($hitPosition / ($hitPosition * $hitPosition));
+        }
+      }
+
+      if($searchHits > 0){
+        if(!is_null($searchScoreKey)){
+          $document[$searchScoreKey] = $searchScore;
+        }
+      } else {
+        unset($found[$foundKey]);
+      }
+    }
+  }
+
+  /**
+   * @param array $found
+   * @param array $havingConditions
+   * @throws InvalidArgumentException
+   */
+  private static function handleHaving(array &$found, array $havingConditions){
+    if(empty($havingConditions)){
+      return;
+    }
+
+    foreach ($found as $key => $document){
+      if(false === ConditionsHandler::handleWhereConditions($havingConditions, $document)){
+        unset($found[$key]);
+      }
+    }
+  }
+
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/DocumentReducer.php b/core/class/sleekDB/Classes/DocumentReducer.php
new file mode 100644
index 00000000..d8615663
--- /dev/null
+++ b/core/class/sleekDB/Classes/DocumentReducer.php
@@ -0,0 +1,665 @@
+<?php
+
+
+namespace SleekDB\Classes;
+
+
+use Closure;
+use SleekDB\Exceptions\InvalidArgumentException;
+use SleekDB\Exceptions\IOException;
+use SleekDB\QueryBuilder;
+use SleekDB\SleekDB;
+
+/**
+ * Class DocumentReducer
+ * Alters one or multiple documents
+ */
+class DocumentReducer
+{
+
+  const SELECT_FUNCTIONS = [
+    "AVG" => "avg",
+    "MAX" => "max",
+    "MIN" => "min",
+    "SUM" => "sum",
+    "ROUND" => "round",
+    "ABS" => "abs",
+    "POSITION" => "position",
+    "UPPER" => "upper",
+    "LOWER" => "lower",
+    "LENGTH" => "length",
+    "CONCAT" => "concat",
+    "CUSTOM" => "custom",
+  ];
+
+  const SELECT_FUNCTIONS_THAT_REDUCE_RESULT = [
+    "AVG" => "avg",
+    "MAX" => "max",
+    "MIN" => "min",
+    "SUM" => "sum"
+  ];
+
+  /**
+   * @param array $found
+   * @param array $fieldsToExclude
+   */
+  public static  function excludeFields(array &$found, array $fieldsToExclude){
+    if (empty($fieldsToExclude)) {
+      return;
+    }
+    foreach ($found as $key => &$document) {
+      if(!is_array($document)){
+        continue;
+      }
+      foreach ($fieldsToExclude as $fieldToExclude) {
+        NestedHelper::removeNestedField($document, $fieldToExclude);
+      }
+    }
+  }
+
+  /**
+   * @param array $results
+   * @param array $listOfJoins
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public static function joinData(array &$results, array $listOfJoins){
+    if(empty($listOfJoins)){
+      return;
+    }
+    // Join data.
+    foreach ($results as $key => $doc) {
+      foreach ($listOfJoins as $join) {
+        // Execute the child query.
+        $joinQuery = ($join['joinFunction'])($doc); // QueryBuilder or result of fetch
+        $propertyName = $join['propertyName'];
+
+        // TODO remove SleekDB check in version 3.0
+        if($joinQuery instanceof QueryBuilder || $joinQuery instanceof SleekDB){
+          $joinResult = $joinQuery->getQuery()->fetch();
+        } else if(is_array($joinQuery)){
+          // user already fetched the query in the join query function
+          $joinResult = $joinQuery;
+        } else {
+          throw new InvalidArgumentException("Invalid join query.");
+        }
+
+        // Add child documents with the current document.
+        $results[$key][$propertyName] = $joinResult;
+      }
+    }
+  }
+
+  /**
+   * @param array $found
+   * @param array $groupBy
+   * @param array $fieldsToSelect
+   * @throws InvalidArgumentException
+   */
+  public static function handleGroupBy(array &$found, array $groupBy, array $fieldsToSelect)
+  {
+    if(empty($groupBy)){
+      return;
+    }
+    // TODO optimize algorithm if possible
+    $groupByFields = $groupBy["groupByFields"];
+    $countKeyName = $groupBy["countKeyName"];
+    $allowEmpty = $groupBy["allowEmpty"];
+
+    $hasSelectFunctionThatNotReduceResult = false;
+    $hasSelectFunctionThatReduceResult = false;
+
+    $pattern = (!empty($fieldsToSelect))? $fieldsToSelect : $groupByFields;
+
+    if(!empty($countKeyName) && empty($fieldsToSelect)){
+      $pattern[] = $countKeyName;
+    }
+
+    // remove duplicates
+    $patternWithOutDuplicates = [];
+    foreach ($pattern as $key => $value){
+      if(array_key_exists($key, $patternWithOutDuplicates) && in_array($value, $patternWithOutDuplicates, true)){
+        continue;
+      }
+      $patternWithOutDuplicates[$key] = $value;
+
+      // validate pattern
+      if(!is_string($key) && !is_string($value)){
+        throw new InvalidArgumentException("You need to format the select correctly when using Group By.");
+      }
+      if(!is_string($value)) {
+
+        if($value instanceof Closure){
+          if($hasSelectFunctionThatNotReduceResult === false){
+            $hasSelectFunctionThatNotReduceResult = true;
+          }
+          if(!in_array($key, $groupByFields, true)){ // key is fieldAlias
+            throw new InvalidArgumentException("You can not select a field \"$key\" that is not grouped by.");
+          }
+          continue;
+        }
+
+        if (!is_array($value) || empty($value)) {
+          throw new InvalidArgumentException("You need to format the select correctly when using Group By.");
+        }
+
+        list($function) = array_keys($value);
+        $functionParameters = $value[$function];
+        self::getFieldNamesOfSelectFunction($function, $functionParameters);
+
+        if(is_string($function) ){
+          if(!in_array(strtolower($function), self::SELECT_FUNCTIONS_THAT_REDUCE_RESULT)){
+            if($hasSelectFunctionThatNotReduceResult === false){
+              $hasSelectFunctionThatNotReduceResult = true;
+            }
+            if(!in_array($key, $groupByFields, true)){ // key is fieldAlias
+              throw new InvalidArgumentException("You can not select a field \"$key\" that is not grouped by.");
+            }
+          } else if($hasSelectFunctionThatReduceResult === false){
+            $hasSelectFunctionThatReduceResult = true;
+          }
+        }
+      } else if($value !== $countKeyName && !in_array($value, $groupByFields, true)) {
+        throw new InvalidArgumentException("You can not select a field that is not grouped by.");
+      }
+    }
+    $pattern = $patternWithOutDuplicates;
+    unset($patternWithOutDuplicates);
+
+    // Apply select functions that do not reduce result before grouping
+    if($hasSelectFunctionThatNotReduceResult){
+      foreach ($found as &$document){
+        foreach ($pattern as $key => $value){
+          if(is_array($value)){
+            list($function) = array_keys($value);
+            $functionParameters = $value[$function];
+            if(in_array(strtolower($function), self::SELECT_FUNCTIONS_THAT_REDUCE_RESULT)){
+              continue;
+            }
+
+            $document[$key] = self::handleSelectFunction($function, $document, $functionParameters);
+          } else if($value instanceof Closure){
+            $function = self::SELECT_FUNCTIONS['CUSTOM'];
+            $functionParameters = $value;
+            $document[$key] = self::handleSelectFunction($function, $document, $functionParameters);
+          }
+        }
+      }
+      unset($document);
+    }
+
+    // GROUP
+    $groupedResult = [];
+    foreach ($found as $foundKey => $document){
+
+      // Prepare hash for group by
+      $values = [];
+      $isEmptyAndEmptyNotAllowed = false;
+      foreach ($groupByFields as $groupByField){
+        $value = NestedHelper::getNestedValue($groupByField, $document);
+        if($allowEmpty === false && is_null($value)){
+          $isEmptyAndEmptyNotAllowed = true;
+          break;
+        }
+        $values[$groupByField] = $value;
+      }
+      if($isEmptyAndEmptyNotAllowed === true){
+        continue;
+      }
+      $valueHash = md5(json_encode($values));
+
+      // is new entry
+      if(!array_key_exists($valueHash, $groupedResult)){
+        $resultDocument = [];
+        foreach ($pattern as $key => $patternValue){
+          $resultFieldName = (is_string($key)) ? $key : $patternValue;
+
+          if($resultFieldName === $countKeyName){
+            // is a counter
+            $attributeValue = 1;
+          } else if(!is_string($patternValue)){
+            // is a function
+            list($function) = array_keys($patternValue);
+            if(in_array(strtolower($function), self::SELECT_FUNCTIONS_THAT_REDUCE_RESULT)){
+              // is a select function that reduce result.
+              $fieldNameToHandle = $patternValue[$function];
+              $currentFieldValue = NestedHelper::getNestedValue($fieldNameToHandle, $document);
+              if(!is_numeric($currentFieldValue)){
+                $attributeValue = [$function => [null]];
+              } else {
+                $attributeValue = [$function => [$currentFieldValue]];
+              }
+            } else {
+              // is a select function that does not reduce result.
+              $attributeValue = $document[$resultFieldName];
+            }
+          } else {
+            // is a normal select
+            $attributeValue = NestedHelper::getNestedValue($patternValue, $document);
+          }
+          $resultDocument[$resultFieldName] = $attributeValue;
+        }
+        $groupedResult[$valueHash] = $resultDocument;
+        continue;
+      }
+
+      // entry exists
+      $currentResult = $groupedResult[$valueHash];
+      foreach ($pattern as $key => $patternValue){
+        $resultFieldName = (is_string($key)) ? $key : $patternValue;
+
+        if($resultFieldName === $countKeyName){
+          $currentResult[$resultFieldName] += 1;
+          continue;
+        }
+
+        if(is_array($patternValue)){
+          list($function) = array_keys($patternValue);
+          if(in_array(strtolower($function), self::SELECT_FUNCTIONS_THAT_REDUCE_RESULT)){
+            $fieldNameToHandle = $patternValue[$function];
+            $currentFieldValue = NestedHelper::getNestedValue($fieldNameToHandle, $document);
+            $currentFieldValue = is_numeric($currentFieldValue) ? $currentFieldValue : null;
+            $currentResult[$resultFieldName][$function][] = $currentFieldValue;
+          }
+        }
+      }
+      $groupedResult[$valueHash] = $currentResult;
+    }
+
+    // Apply select functions that reduce result
+    if($hasSelectFunctionThatReduceResult){
+      foreach ($groupedResult as &$document){
+        foreach ($pattern as $key => $value){
+          if(!is_array($value)){
+            continue;
+          }
+          list($function) = array_keys($value);
+          if(!in_array(strtolower($function), self::SELECT_FUNCTIONS_THAT_REDUCE_RESULT)){
+            continue;
+          }
+          // "price" => ["sum" => [...]]
+          $functionParameters = $key.".".$function;
+          $document[$key] = self::handleSelectFunction($function, $document, $functionParameters);
+        }
+      }
+      unset($document);
+    }
+
+    $found = array_values($groupedResult);
+  }
+
+  /**
+   * @param array $found
+   * @param string $primaryKey
+   * @param array $fieldsToSelect
+   * @throws InvalidArgumentException
+   */
+  public static function selectFields(array &$found, string $primaryKey, array $fieldsToSelect)
+  {
+    if (empty($fieldsToSelect)) {
+      return;
+    }
+
+    $functionsThatReduceResultToSingleResult = self::SELECT_FUNCTIONS_THAT_REDUCE_RESULT;
+    $reducedResult = []; // "fieldName" => ["values",...]
+    $reduceResultToSingleResult = false;
+
+    // check if result should be reduced to single result
+    foreach ($fieldsToSelect as $fieldToSelect){
+      if(!is_array($fieldToSelect)){
+        continue;
+      }
+
+      list($function) = array_keys($fieldToSelect);
+
+      if(in_array(strtolower($function), $functionsThatReduceResultToSingleResult, true)){
+        $reduceResultToSingleResult = true;
+      }
+
+      if($reduceResultToSingleResult === true){
+        break;
+      }
+    }
+
+    // Is not result of group by and contains function that reduces result to single result
+    if($reduceResultToSingleResult === true){
+      foreach ($found as $key => $document) {
+        foreach ($fieldsToSelect as $fieldAlias => $fieldToSelect) {
+          $fieldName = (!is_int($fieldAlias))? $fieldAlias : $fieldToSelect;
+          if(!is_array($fieldToSelect)){
+            continue;
+          }
+
+          // no alias specified and select function (array) used as element
+          if(!is_string($fieldName)){
+            $errorMsg = "You need to specify an alias for the field when using select functions.";
+            throw new InvalidArgumentException($errorMsg);
+          }
+
+          list($function) = array_keys($fieldToSelect);
+          $functionParameters = $fieldToSelect[$function];
+
+          if(in_array(strtolower($function), $functionsThatReduceResultToSingleResult, true)){
+            if(!is_string($functionParameters)){
+              $errorMsg = "When using the function \"$function\" the parameter has to be a string (fieldName).";
+              throw new InvalidArgumentException($errorMsg);
+            }
+
+            $value = NestedHelper::getNestedValue($functionParameters, $document);
+            if(!array_key_exists($fieldName, $reducedResult)){
+              $reducedResult[$fieldName] = [];
+            }
+            $reducedResult[$fieldName][] = $value;
+          }
+        }
+      }
+
+      $newDocument = [];
+      foreach ($fieldsToSelect as $fieldAlias => $fieldToSelect){
+        $fieldName = (!is_int($fieldAlias))? $fieldAlias : $fieldToSelect;
+        if(!is_array($fieldToSelect)){
+          continue;
+        }
+
+        list($function) = array_keys($fieldToSelect);
+        if(in_array(strtolower($function), $functionsThatReduceResultToSingleResult, true)){
+          $newDocument[$fieldName] = self::handleSelectFunction($function, $reducedResult, $fieldName);
+        }
+      }
+      $found = [$newDocument];
+      return;
+    }
+
+    // result should not be reduced to single result
+
+    foreach ($found as $key => &$document) {
+      $newDocument = [];
+
+      $newDocument[$primaryKey] = $document[$primaryKey];
+      foreach ($fieldsToSelect as $fieldAlias => $fieldToSelect) {
+
+        $fieldName = (!is_int($fieldAlias))? $fieldAlias : $fieldToSelect;
+
+        if(!is_string($fieldToSelect) && !is_int($fieldToSelect) && !is_array($fieldToSelect)
+          && !($fieldToSelect instanceof Closure))
+        {
+          $errorMsg = "When using select an array containing fieldNames as strings or select functions has to be given";
+          throw new InvalidArgumentException($errorMsg);
+        }
+
+        // no alias specified and select function (array) used as element
+        if(!is_string($fieldName)){
+          $errorMsg = "You need to specify an alias for the field when using select functions.";
+          throw new InvalidArgumentException($errorMsg);
+        }
+
+        // if the fieldToSelect is an array, the user wants to use a select function
+        if(is_array($fieldToSelect)){
+          // "fieldAlias" => ["function" => "field"]
+          list($function) = array_keys($fieldToSelect);
+          $functionParameters = $fieldToSelect[$function];
+          $newDocument[$fieldName] = self::handleSelectFunction($function, $document, $functionParameters);
+        } else if($fieldToSelect instanceof Closure){
+          $function = self::SELECT_FUNCTIONS['CUSTOM'];
+          $functionParameters = $fieldToSelect;
+          $newDocument[$fieldName] = self::handleSelectFunction($function, $document, $functionParameters);
+        } else {
+          // No select function is used (fieldToSelect is string or int)
+          $fieldValue = NestedHelper::getNestedValue((string) $fieldToSelect, $document);
+          $createdArray = NestedHelper::createNestedArray($fieldName, $fieldValue);
+          if(!empty($createdArray)){
+            $createdArrayKey = array_keys($createdArray)[0];
+            $newDocument[$createdArrayKey] = $createdArray[$createdArrayKey];
+          }
+        }
+      }
+      $document = $newDocument;
+    }
+  }
+
+  /**
+   * @param string $function
+   * @param array $document
+   * @param string|array|int|Closure $functionParameters
+   * @return mixed
+   * @throws InvalidArgumentException
+   */
+  private static function handleSelectFunction(string $function, array $document, $functionParameters){
+
+    if(is_int($functionParameters)){
+      $functionParameters = (string) $functionParameters;
+    }
+
+    switch (strtolower($function)){
+      case self::SELECT_FUNCTIONS["ROUND"]:
+        list($field, $precision) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        if(!is_string($field) || !is_int($precision)){
+          $errorMsg = "When using the select function \"$function\" the field parameter has to be a string "
+            ."and the precision parameter has to be an integer";
+          throw new InvalidArgumentException($errorMsg);
+        }
+
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_numeric($data)){
+          return null;
+        }
+        return round((float) $data, $precision);
+      case self::SELECT_FUNCTIONS["ABS"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_numeric($data)){
+          return null;
+        }
+        return abs($data);
+      case self::SELECT_FUNCTIONS["POSITION"]:
+        list($field, $subString) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        if(!is_string($subString) || !is_string($field)){
+          $errorMsg = "When using the select function \"$function\" the subString and field parameters has to be strings";
+          throw new InvalidArgumentException($errorMsg);
+        }
+
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_string($data)){
+          return null;
+        }
+        $result = strpos($data, $subString);
+        return ($result !== false)? $result + 1 : null;
+      case self::SELECT_FUNCTIONS["UPPER"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_string($data)){
+          return null;
+        }
+        return strtoupper($data);
+      case self::SELECT_FUNCTIONS["LOWER"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_string($data)){
+          return null;
+        }
+        return strtolower($data);
+      case self::SELECT_FUNCTIONS["LENGTH"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(is_string($data)){
+          return strlen($data);
+        }
+        if(is_array($data)){
+          return count($data);
+        }
+        return null;
+      case self::SELECT_FUNCTIONS["CONCAT"]:
+        list($fields, $glue) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $result = "";
+        foreach ($fields as $field){
+          $data = NestedHelper::getNestedValue($field, $document);
+          // convertible to string
+          if(
+            ( !is_array( $data ) )
+            && ($data !== "" && $data !== null)
+            && (
+              ( !is_object( $data ) && settype( $data, 'string' ) !== false )
+              || ( is_object( $data ) && method_exists( $data, '__toString' ) )
+            )
+          )
+          {
+            if($result !== ""){
+              $result .= $glue;
+            }
+            $result .= $data;
+          }
+        }
+        return ($result !== "") ? $result : null;
+      case self::SELECT_FUNCTIONS["SUM"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_array($data)){
+          return null;
+        }
+
+        $result = 0;
+        $allEntriesNull = true;
+        foreach ($data as $value){
+          if(!is_null($value)){
+            $result += $value;
+            $allEntriesNull = false;
+          }
+        }
+        if($allEntriesNull === true){
+          return null;
+        }
+        return $result;
+      case self::SELECT_FUNCTIONS["MIN"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_array($data)){
+          return null;
+        }
+
+        $result = INF;
+        $allEntriesNull = true;
+        foreach ($data as $value){
+          if(!is_null($value)){
+            if($value < $result){
+              $result = $value;
+            }
+            $allEntriesNull = false;
+          }
+        }
+        if($allEntriesNull === true){
+          return null;
+        }
+        return $result;
+      case self::SELECT_FUNCTIONS["MAX"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_array($data)){
+          return null;
+        }
+
+        $result = -INF;
+        $allEntriesNull = true;
+        foreach ($data as $value){
+          if($value > $result && !is_null($value)) {
+            $result = $value;
+            $allEntriesNull = false;
+          }
+        }
+        if($allEntriesNull === true){
+          return null;
+        }
+        return $result;
+      case self::SELECT_FUNCTIONS["AVG"]:
+        list($field) = self::getFieldNamesOfSelectFunction($function, $functionParameters);
+        $data = NestedHelper::getNestedValue($field, $document);
+        if(!is_array($data)){
+          return null;
+        }
+
+        $result = 0;
+        $resultValueAmount = (count($data) + 1);
+        $allEntriesNull = true;
+        foreach ($data as $value){
+          if(!is_null($value)){
+            $result += $value;
+            $allEntriesNull = false;
+          }
+        }
+        if($allEntriesNull === true){
+          return null;
+        }
+        return ($result / $resultValueAmount);
+      case self::SELECT_FUNCTIONS['CUSTOM']:
+        if(!($functionParameters instanceof Closure)){
+          throw new InvalidArgumentException("When using a custom select function you need to provide a closure.");
+        }
+        return $functionParameters($document);
+      default:
+        throw new InvalidArgumentException("The given select function \"$function\" is not supported.");
+    }
+  }
+
+  /**
+   * @param string $function
+   * @param string|array|int $functionParameters
+   * @return array [array|string $fieldNames, $addition]
+   * @throws InvalidArgumentException
+   */
+  private static function getFieldNamesOfSelectFunction(string $function, $functionParameters): array
+  {
+    if(is_int($functionParameters)){
+      $functionParameters = (string) $functionParameters;
+    }
+    $function = strtolower($function);
+    switch ($function){
+      case self::SELECT_FUNCTIONS["ROUND"]:
+      case self::SELECT_FUNCTIONS["POSITION"]:
+        if(!is_array($functionParameters) || count($functionParameters) !== 2){
+          $type = gettype($functionParameters);
+          $length = (is_array($functionParameters)) ? count($functionParameters) : 0;
+          $errorMsg = "When using the select function \"$function\" the parameter "
+            ."has to be an array with length = 2, got $type with length $length";
+          throw new InvalidArgumentException($errorMsg);
+        }
+        list($firstParameter, $secondParameter) = $functionParameters;
+        if($function === self::SELECT_FUNCTIONS["ROUND"]){
+          $field = $firstParameter;
+          $addition = $secondParameter;
+        } else {
+          $field = $secondParameter;
+          $addition = $firstParameter;
+        }
+        return [$field, $addition];
+      case self::SELECT_FUNCTIONS["ABS"]:
+      case self::SELECT_FUNCTIONS["UPPER"]:
+      case self::SELECT_FUNCTIONS["LOWER"]:
+      case self::SELECT_FUNCTIONS["LENGTH"]:
+      case self::SELECT_FUNCTIONS["SUM"]:
+      case self::SELECT_FUNCTIONS["MIN"]:
+      case self::SELECT_FUNCTIONS["MAX"]:
+      case self::SELECT_FUNCTIONS["AVG"]:
+        if(!is_string($functionParameters)){
+          $type = gettype($functionParameters);
+          $errorMsg = "When using the select function \"$function\" the parameter "
+            ."has to be a string, got $type.";
+          throw new InvalidArgumentException($errorMsg);
+        }
+        return [$functionParameters, null];
+      case self::SELECT_FUNCTIONS["CONCAT"]:
+        if(!is_array($functionParameters) || count($functionParameters) < 3){
+          $type = gettype($functionParameters);
+          $length = (is_array($functionParameters)) ? count($functionParameters) : 0;
+          $errorMsg = "When using the select function \"$function\" the parameter "
+            ."has to be an array with length > 3, got $type with length $length";
+          throw new InvalidArgumentException($errorMsg);
+        }
+        list($glue) = $functionParameters;
+        unset($functionParameters[array_keys($functionParameters)[0]]);
+
+        return [$functionParameters, $glue];
+      default:
+        throw new InvalidArgumentException("The given select function \"$function\" is not supported.");
+    }
+  }
+
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/DocumentUpdater.php b/core/class/sleekDB/Classes/DocumentUpdater.php
new file mode 100644
index 00000000..20fd98c2
--- /dev/null
+++ b/core/class/sleekDB/Classes/DocumentUpdater.php
@@ -0,0 +1,159 @@
+<?php
+
+
+namespace SleekDB\Classes;
+
+
+use SleekDB\Exceptions\InvalidArgumentException;
+use SleekDB\Exceptions\IOException;
+use SleekDB\Query;
+use SleekDB\Store;
+
+/**
+ * Class DocumentUpdater
+ * Update and/or delete documents
+ */
+class DocumentUpdater
+{
+
+  protected $storePath;
+  protected $primaryKey;
+
+  public function __construct(string $storePath, string $primaryKey)
+  {
+    $this->storePath = $storePath;
+    $this->primaryKey = $primaryKey;
+  }
+
+  /**
+   * Update one or multiple documents, based on current query
+   * @param array $results
+   * @param array $updatable
+   * @param bool $returnUpdatedDocuments
+   * @return array|bool
+   * @throws IOException
+   */
+  public function updateResults(array $results, array $updatable, bool $returnUpdatedDocuments)
+  {
+    if(count($results) === 0) {
+      return false;
+    }
+
+    $primaryKey = $this->primaryKey;
+    $dataPath = $this->getDataPath();
+    // check if all documents exist beforehand
+    foreach ($results as $key => $data) {
+      $primaryKeyValue = IoHelper::secureStringForFileAccess($data[$primaryKey]);
+      $data[$primaryKey] = (int) $primaryKeyValue;
+      $results[$key] = $data;
+
+      $filePath = $dataPath . $primaryKeyValue . '.json';
+      if(!file_exists($filePath)){
+        return false;
+      }
+    }
+
+    foreach ($results as $key => $data){
+      $filePath = $dataPath . $data[$primaryKey] . '.json';
+      foreach ($updatable as $fieldName => $value) {
+        // Do not update the primary key reserved index of a store.
+        if ($fieldName !== $primaryKey) {
+          NestedHelper::updateNestedValue($fieldName, $data, $value);
+        }
+      }
+      IoHelper::writeContentToFile($filePath, json_encode($data));
+      $results[$key] = $data;
+    }
+    return ($returnUpdatedDocuments === true) ? $results : true;
+  }
+
+  /**
+   * Deletes matched store objects.
+   * @param array $results
+   * @param int $returnOption
+   * @return bool|array|int
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function deleteResults(array $results, int $returnOption)
+  {
+    $primaryKey = $this->primaryKey;
+    $dataPath = $this->getDataPath();
+    switch ($returnOption){
+      case Query::DELETE_RETURN_BOOL:
+        $returnValue = !empty($results);
+        break;
+      case Query::DELETE_RETURN_COUNT:
+        $returnValue = count($results);
+        break;
+      case Query::DELETE_RETURN_RESULTS:
+        $returnValue = $results;
+        break;
+      default:
+        throw new InvalidArgumentException("Return option \"$returnOption\" is not supported");
+    }
+
+    if (empty($results)) {
+      return $returnValue;
+    }
+
+    // TODO implement beforehand check
+
+    foreach ($results as $key => $data) {
+      $primaryKeyValue = IoHelper::secureStringForFileAccess($data[$primaryKey]);
+      $filePath = $dataPath . $primaryKeyValue . '.json';
+      if(false === IoHelper::deleteFile($filePath)){
+        throw new IOException(
+          'Unable to delete document! 
+            Already deleted documents: '.$key.'. 
+            Location: "' . $filePath .'"'
+        );
+      }
+    }
+    return $returnValue;
+  }
+
+  /**
+   * @param array $results
+   * @param array $fieldsToRemove
+   * @return array|false
+   * @throws IOException
+   */
+  public function removeFields(array &$results, array $fieldsToRemove)
+  {
+    $primaryKey = $this->primaryKey;
+    $dataPath = $this->getDataPath();
+
+    // check if all documents exist beforehand
+    foreach ($results as $key => $data) {
+      $primaryKeyValue = IoHelper::secureStringForFileAccess($data[$primaryKey]);
+      $data[$primaryKey] = $primaryKeyValue;
+      $results[$key] = $data;
+
+      $filePath = $dataPath . $primaryKeyValue . '.json';
+      if(!file_exists($filePath)){
+        return false;
+      }
+    }
+
+    foreach ($results as &$document){
+      foreach ($fieldsToRemove as $fieldToRemove){
+        if($fieldToRemove !== $primaryKey){
+          NestedHelper::removeNestedField($document, $fieldToRemove);
+        }
+      }
+      $filePath = $dataPath . $document[$primaryKey] . '.json';
+      IoHelper::writeContentToFile($filePath, json_encode($document));
+    }
+    return $results;
+  }
+
+  /**
+   * @return string
+   */
+  private function getDataPath(): string
+  {
+    return $this->storePath . Store::dataDirectory;
+  }
+
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/IoHelper.php b/core/class/sleekDB/Classes/IoHelper.php
new file mode 100644
index 00000000..376b53b5
--- /dev/null
+++ b/core/class/sleekDB/Classes/IoHelper.php
@@ -0,0 +1,251 @@
+<?php
+
+namespace SleekDB\Classes;
+
+use Closure;
+use Exception;
+use RecursiveDirectoryIterator;
+use RecursiveIteratorIterator;
+use SleekDB\Exceptions\IOException;
+use SleekDB\Exceptions\JsonException;
+
+/**
+ * Class IoHelper
+ * Helper to handle file input/ output.
+ */
+class IoHelper {
+
+  /**
+   * @param string $path
+   * @throws IOException
+   */
+  public static function checkWrite(string $path)
+  {
+    if(file_exists($path) === false){
+      $path = dirname($path);
+    }
+    // Check if PHP has write permission
+    if (!is_writable($path)) {
+      throw new IOException(
+        "Directory or file is not writable at \"$path\". Please change permission."
+      );
+    }
+  }
+
+  /**
+   * @param string $path
+   * @throws IOException
+   */
+  public static function checkRead(string $path)
+  {
+    // Check if PHP has read permission
+    if (!is_readable($path)) {
+      throw new IOException(
+        "Directory or file is not readable at \"$path\". Please change permission."
+      );
+    }
+  }
+
+    /**
+     * @param string $filePath
+     * @return string
+     * @throws IOException
+     */
+  public static function getFileContent(string $filePath): string
+  {
+
+    self::checkRead($filePath);
+
+    if(!file_exists($filePath)) {
+      throw new IOException("File does not exist: $filePath");
+    }
+
+    $content = false;
+    $fp = fopen($filePath, 'rb');
+    if(flock($fp, LOCK_SH)){
+      $content = stream_get_contents($fp);
+    }
+    flock($fp, LOCK_UN);
+    fclose($fp);
+
+    if($content === false) {
+      throw new IOException("Could not retrieve the content of a file. Please check permissions at: $filePath");
+    }
+
+    return $content;
+  }
+
+  /**
+   * @param string $filePath
+   * @param string $content
+   * @throws IOException
+   */
+  public static function writeContentToFile(string $filePath, string $content){
+
+    self::checkWrite($filePath);
+
+    // Wait until it's unlocked, then write.
+    if(file_put_contents($filePath, $content, LOCK_EX) === false){
+      throw new IOException("Could not write content to file. Please check permissions at: $filePath");
+    }
+  }
+
+  /**
+   * @param string $folderPath
+   * @return bool
+   * @throws IOException
+   */
+  public static function deleteFolder(string $folderPath): bool
+  {
+    self::checkWrite($folderPath);
+    $it = new RecursiveDirectoryIterator($folderPath, RecursiveDirectoryIterator::SKIP_DOTS);
+    $files = new RecursiveIteratorIterator($it, RecursiveIteratorIterator::CHILD_FIRST);
+    foreach ($files as $file) {
+      self::checkWrite($file);
+      if ($file->isDir()) {
+        rmdir($file->getRealPath());
+      } else {
+        unlink($file->getRealPath());
+      }
+    }
+    return rmdir($folderPath);
+  }
+
+  /**
+   * @param string $folderPath
+   * @throws IOException
+   */
+  public static function createFolder(string $folderPath){
+    // We don't need to create a folder if it already exists.
+    if(file_exists($folderPath) === true){
+      return;
+    }
+    self::checkWrite($folderPath);
+    // Check if the data_directory exists or create one.
+    if (!file_exists($folderPath) && !mkdir($folderPath, 0777, true) && !is_dir($folderPath)) {
+      throw new IOException(
+        'Unable to create the a directory at ' . $folderPath
+      );
+    }
+  }
+
+  /**
+   * @param string $filePath
+   * @param Closure $updateContentFunction Has to return a string or an array that will be encoded to json.
+   * @return string
+   * @throws IOException
+   * @throws JsonException
+   */
+  public static function updateFileContent(string $filePath, Closure $updateContentFunction): string
+  {
+    self::checkRead($filePath);
+    self::checkWrite($filePath);
+
+    $content = false;
+
+    $fp = fopen($filePath, 'rb');
+    if(flock($fp, LOCK_SH)){
+      $content = stream_get_contents($fp);
+    }
+    flock($fp, LOCK_UN);
+    fclose($fp);
+
+    if($content === false){
+      throw new IOException("Could not get shared lock for file: $filePath");
+    }
+
+    $content = $updateContentFunction($content);
+
+    if(!is_string($content)){
+      $encodedContent = json_encode($content);
+      if($encodedContent === false){
+        $content = (!is_object($content) && !is_array($content) && !is_null($content)) ? $content : gettype($content);
+        throw new JsonException("Could not encode content with json_encode. Content: \"$content\".");
+      }
+      $content = $encodedContent;
+    }
+
+
+    if(file_put_contents($filePath, $content, LOCK_EX) === false){
+      throw new IOException("Could not write content to file. Please check permissions at: $filePath");
+    }
+
+
+    return $content;
+  }
+
+  /**
+   * @param string $filePath
+   * @return bool
+   */
+  public static function deleteFile(string $filePath): bool
+  {
+
+    if(false === file_exists($filePath)){
+      return true;
+    }
+    try{
+      self::checkWrite($filePath);
+    }catch(Exception $exception){
+      return false;
+    }
+
+    return (@unlink($filePath) && !file_exists($filePath));
+  }
+
+  /**
+   * @param array $filePaths
+   * @return bool
+   */
+  public static function deleteFiles(array $filePaths): bool
+  {
+    foreach ($filePaths as $filePath){
+      // if a file does not exist, we do not need to delete it.
+      if(true === file_exists($filePath)){
+        try{
+          self::checkWrite($filePath);
+          if(false === @unlink($filePath) || file_exists($filePath)){
+            return false;
+          }
+        } catch (Exception $exception){
+          // TODO trigger a warning or exception
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Strip string for secure file access.
+   * @param string $string
+   * @return string
+   */
+  public static function secureStringForFileAccess(string $string): string
+  {
+    return (str_replace(array(".", "/", "\\"), "", $string));
+  }
+
+  /**
+   * Appends a slash ("/") to the given directory path if there is none.
+   * @param string $directory
+   */
+  public static function normalizeDirectory(string &$directory){
+    if(!empty($directory) && substr($directory, -1) !== "/") {
+      $directory .= "/";
+    }
+  }
+
+  /**
+   * Returns the amount of files in folder.
+   * @param string $folder
+   * @return int
+   * @throws IOException
+   */
+  public static function countFolderContent(string $folder): int
+  {
+    self::checkRead($folder);
+    $fi = new \FilesystemIterator($folder, \FilesystemIterator::SKIP_DOTS);
+    return iterator_count($fi);
+  }
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Classes/NestedHelper.php b/core/class/sleekDB/Classes/NestedHelper.php
new file mode 100644
index 00000000..6c1979fc
--- /dev/null
+++ b/core/class/sleekDB/Classes/NestedHelper.php
@@ -0,0 +1,140 @@
+<?php
+
+
+namespace SleekDB\Classes;
+
+
+use SleekDB\Exceptions\InvalidArgumentException;
+
+/**
+ * Class NestedHelper
+ * Helper to handle arrays.
+ */
+class NestedHelper
+{
+
+  /**
+   * Get nested properties of a store object.
+   * @param string $fieldName
+   * @param array $data
+   * @return mixed
+   * @throws InvalidArgumentException
+   */
+  public static function getNestedValue(string $fieldName, array $data)
+  {
+    $fieldName = trim($fieldName);
+    if (empty($fieldName)) {
+      throw new InvalidArgumentException('fieldName is not allowed to be empty');
+    }
+    // Dive deep step by step.
+    foreach (explode('.', $fieldName) as $i) {
+      // If the field does not exists we return null;
+      if (!isset($data[$i])) {
+        return null;
+      }
+      // The index is valid, collect the data.
+      $data = $data[$i];
+    }
+    return $data;
+  }
+
+  /**
+   * Check if a nested Property exists
+   * @param string $fieldName
+   * @param array $data
+   * @return mixed
+   * @throws InvalidArgumentException
+   */
+  public static function nestedFieldExists(string $fieldName, array $data)
+  {
+    $fieldName = trim($fieldName);
+    if (empty($fieldName)) {
+      throw new InvalidArgumentException('fieldName is not allowed to be empty');
+    }
+
+    // Dive deep step by step.
+    foreach (explode('.', $fieldName) as $i) {
+      // check if field exists
+      if (!is_array($data) || !array_key_exists($i, $data)) {
+        return false;
+      }
+      // The index is valid, dive deeper.
+      $data = $data[$i];
+    }
+    return true;
+  }
+
+  public static function updateNestedValue(string $fieldName, array &$data, $newValue){
+    $fieldNameArray = explode(".", $fieldName);
+    $value = $newValue;
+    if(count($fieldNameArray) > 1){
+      $data = self::_updateNestedValueHelper($fieldNameArray, $data, $newValue, count($fieldNameArray));
+      return;
+    }
+    $data[$fieldNameArray[0]] = $value;
+  }
+
+  public static function createNestedArray(string $fieldName, $fieldValue): array
+  {
+    $temp = [];
+    $fieldNameArray = explode('.', $fieldName);
+    $fieldNameArrayReverse = array_reverse($fieldNameArray);
+    foreach ($fieldNameArrayReverse as $index => $i) {
+      if($index === 0){
+        $temp = array($i => $fieldValue);
+      } else {
+        $temp = array($i => $temp);
+      }
+    }
+
+    return $temp;
+  }
+
+  public static function removeNestedField(array &$document, string $fieldToRemove){
+    if (array_key_exists($fieldToRemove, $document)) {
+      unset($document[$fieldToRemove]);
+      return;
+    }
+    // should be a nested array at this point
+    $temp = &$document;
+    $fieldNameArray = explode('.', $fieldToRemove);
+    $fieldNameArrayCount = count($fieldNameArray);
+    foreach ($fieldNameArray as $index => $i) {
+      // last iteration
+      if(($fieldNameArrayCount - 1) === $index){
+        if(is_array($temp) && array_key_exists($i, $temp)) {
+          unset($temp[$i]);
+        }
+        break;
+      }
+      if(!is_array($temp) || !array_key_exists($i, $temp)){
+        break;
+      }
+      $temp = &$temp[$i];
+    }
+  }
+
+  /**
+   * @param array $keysArray
+   * @param $data
+   * @param $newValue
+   * @param int $originalKeySize
+   * @return mixed
+   */
+  private static function _updateNestedValueHelper(array $keysArray, $data, $newValue, int $originalKeySize)
+  {
+    if(empty($keysArray)){
+      return $newValue;
+    }
+    $currentKey = $keysArray[0];
+    $result = (is_array($data)) ? $data : [];
+    if(!is_array($data) || !array_key_exists($currentKey, $data)){
+      $result[$currentKey] = self::_updateNestedValueHelper(array_slice($keysArray, 1), $data, $newValue, $originalKeySize);
+      if(count($keysArray) !== $originalKeySize){
+        return $result;
+      }
+    }
+    $result[$currentKey] = self::_updateNestedValueHelper(array_slice($keysArray, 1), $data[$currentKey], $newValue, $originalKeySize);
+    return $result;
+  }
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/Exceptions/IOException.php b/core/class/sleekDB/Exceptions/IOException.php
new file mode 100644
index 00000000..cb634625
--- /dev/null
+++ b/core/class/sleekDB/Exceptions/IOException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace SleekDB\Exceptions;
+
+class IOException extends \Exception
+{
+}
diff --git a/core/class/sleekDB/Exceptions/IdNotAllowedException.php b/core/class/sleekDB/Exceptions/IdNotAllowedException.php
new file mode 100644
index 00000000..8061373e
--- /dev/null
+++ b/core/class/sleekDB/Exceptions/IdNotAllowedException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace SleekDB\Exceptions;
+
+class IdNotAllowedException extends \Exception
+{
+}
diff --git a/core/class/sleekDB/Exceptions/InvalidArgumentException.php b/core/class/sleekDB/Exceptions/InvalidArgumentException.php
new file mode 100644
index 00000000..60455065
--- /dev/null
+++ b/core/class/sleekDB/Exceptions/InvalidArgumentException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace SleekDB\Exceptions;
+
+class InvalidArgumentException extends \Exception
+{
+}
diff --git a/core/class/sleekDB/Exceptions/InvalidConfigurationException.php b/core/class/sleekDB/Exceptions/InvalidConfigurationException.php
new file mode 100644
index 00000000..902526cd
--- /dev/null
+++ b/core/class/sleekDB/Exceptions/InvalidConfigurationException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace SleekDB\Exceptions;
+
+class InvalidConfigurationException extends \Exception
+{
+}
diff --git a/core/class/sleekDB/Exceptions/InvalidPropertyAccessException.php b/core/class/sleekDB/Exceptions/InvalidPropertyAccessException.php
new file mode 100644
index 00000000..a78bd6ee
--- /dev/null
+++ b/core/class/sleekDB/Exceptions/InvalidPropertyAccessException.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace SleekDB\Exceptions;
+
+/**
+ * Class InvalidPropertyAccessException
+ * @deprecated since version 2.7.
+ */
+class InvalidPropertyAccessException extends \Exception
+{
+}
diff --git a/core/class/sleekDB/Exceptions/JsonException.php b/core/class/sleekDB/Exceptions/JsonException.php
new file mode 100644
index 00000000..b049fef7
--- /dev/null
+++ b/core/class/sleekDB/Exceptions/JsonException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace SleekDB\Exceptions;
+
+class JsonException extends \Exception
+{
+}
diff --git a/core/class/sleekDB/Query.php b/core/class/sleekDB/Query.php
new file mode 100644
index 00000000..f202264f
--- /dev/null
+++ b/core/class/sleekDB/Query.php
@@ -0,0 +1,192 @@
+<?php
+
+namespace SleekDB;
+
+use SleekDB\Classes\CacheHandler;
+use SleekDB\Classes\DocumentFinder;
+use SleekDB\Classes\DocumentUpdater;
+use SleekDB\Exceptions\InvalidArgumentException;
+use SleekDB\Exceptions\IOException;
+
+/**
+ * Class Query
+ * Query execution object of SleekDB.
+ */
+class Query
+{
+
+  const DELETE_RETURN_BOOL = 1;
+  const DELETE_RETURN_RESULTS = 2;
+  const DELETE_RETURN_COUNT = 3;
+
+  const SEARCH_ALGORITHM = [
+    "hits" => 1,
+    "hits_prioritize" => 2,
+    "prioritize" => 3,
+    "prioritize_position" => 4,
+  ];
+
+  /**
+   * @var CacheHandler|null
+   */
+  protected $cacheHandler;
+
+  /**
+   * @var DocumentFinder
+   */
+  protected $documentFinder;
+
+  /**
+   * @var DocumentUpdater
+   */
+  protected $documentUpdater;
+
+  /**
+   * Query constructor.
+   * @param QueryBuilder $queryBuilder
+   */
+  public function __construct(QueryBuilder $queryBuilder)
+  {
+    $store = $queryBuilder->_getStore();
+    $primaryKey = $store->getPrimaryKey();
+
+    $this->cacheHandler = new CacheHandler($store->getStorePath(), $queryBuilder);
+    $this->documentFinder = new DocumentFinder($store->getStorePath(), $queryBuilder->_getConditionProperties(), $primaryKey);
+    $this->documentUpdater = new DocumentUpdater($store->getStorePath(), $primaryKey);
+  }
+
+  /**
+   * Execute query and get results.
+   * @return array
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function fetch(): array
+  {
+    return $this->getResults();
+  }
+
+  /**
+   * Check if data is found.
+   * @return bool
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function exists(): bool
+  {
+    // Return boolean on data exists check.
+    return !empty($this->first());
+  }
+
+  /**
+   * Return the first document.
+   * @return array empty array or single document
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function first(): array
+  {
+    return $this->getResults(true);
+  }
+
+  /**
+   * Update parts of one or multiple documents based on current query.
+   * @param array $updatable
+   * @param bool $returnUpdatedDocuments
+   * @return array|bool
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function update(array $updatable, bool $returnUpdatedDocuments = false){
+
+    if(empty($updatable)){
+      throw new InvalidArgumentException("You have to define what you want to update.");
+    }
+
+    $results = $this->documentFinder->findDocuments(false, false);
+
+    $this->getCacheHandler()->deleteAllWithNoLifetime();
+
+    return $this->documentUpdater->updateResults($results, $updatable, $returnUpdatedDocuments);
+  }
+
+  /**
+   * Delete one or multiple documents based on current query.
+   * @param int $returnOption
+   * @return bool|array|int
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function delete(int $returnOption = self::DELETE_RETURN_BOOL){
+    $results = $this->documentFinder->findDocuments(false, false);
+
+    $this->getCacheHandler()->deleteAllWithNoLifetime();
+
+    return $this->documentUpdater->deleteResults($results, $returnOption);
+  }
+
+  /**
+   * Remove fields of one or multiple documents based on current query.
+   * @param array $fieldsToRemove
+   * @return array|false
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function removeFields(array $fieldsToRemove)
+  {
+    if(empty($fieldsToRemove)){
+      throw new InvalidArgumentException("You have to define what fields you want to remove.");
+    }
+    $results = $this->documentFinder->findDocuments(false, false);
+
+    $this->getCacheHandler()->deleteAllWithNoLifetime();
+
+    return $this->documentUpdater->removeFields($results, $fieldsToRemove);
+  }
+
+  /**
+   * Retrieve Cache object.
+   * @return Cache
+   */
+  public function getCache(): Cache
+  {
+    return $this->getCacheHandler()->getCache();
+  }
+
+  /**
+   * Retrieve the results from either the cache or store.
+   * @param bool $getOneDocument
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  private function getResults(bool $getOneDocument = false): array
+  {
+
+    $results = $this->getCacheHandler()->getCacheContent($getOneDocument);
+
+    if($results !== null) {
+      return $results;
+    }
+
+    $results = $this->documentFinder->findDocuments($getOneDocument, true);
+
+    if ($getOneDocument === true && count($results) > 0) {
+      list($item) = $results;
+      $results = $item;
+    }
+
+    $this->getCacheHandler()->setCacheContent($results);
+
+    return $results;
+  }
+
+  /**
+   * Retrieve the caching layer bridge.
+   * @return CacheHandler
+   */
+  private function getCacheHandler(): CacheHandler
+  {
+    return $this->cacheHandler;
+  }
+}
\ No newline at end of file
diff --git a/core/class/sleekDB/QueryBuilder.php b/core/class/sleekDB/QueryBuilder.php
new file mode 100644
index 00000000..d9f711fd
--- /dev/null
+++ b/core/class/sleekDB/QueryBuilder.php
@@ -0,0 +1,516 @@
+<?php
+
+namespace SleekDB;
+
+use Closure;
+use SleekDB\Exceptions\InvalidArgumentException;
+
+class QueryBuilder
+{
+
+  /**
+   * @var Store
+   */
+  protected $store;
+  /**
+   * @var Cache
+   */
+  protected $cache;
+
+  protected $whereConditions = [];
+
+  protected $skip = 0;
+  protected $limit = 0;
+  protected $orderBy = [];
+  protected $nestedWhere = []; // TODO remove with version 3.0
+  protected $search = [];
+  protected $searchOptions = [
+    "minLength" => 2,
+    "scoreKey" => "searchScore",
+    "mode" => "or",
+    "algorithm" => Query::SEARCH_ALGORITHM["hits"]
+  ];
+
+  protected $fieldsToSelect = [];
+  protected $fieldsToExclude = [];
+  protected $groupBy = [];
+  protected $havingConditions = [];
+
+  protected $listOfJoins = [];
+  protected $distinctFields = [];
+
+  protected $useCache;
+  protected $regenerateCache = false;
+  protected $cacheLifetime;
+
+
+  // will also not be used for cache token
+  protected $propertiesNotUsedInConditionsArray = [
+    "propertiesNotUsedInConditionsArray",
+    "propertiesNotUsedForCacheToken",
+    "store",
+    "cache",
+  ];
+
+  protected $propertiesNotUsedForCacheToken = [
+    "useCache",
+    "regenerateCache",
+    "cacheLifetime"
+  ];
+
+  /**
+   * QueryBuilder constructor.
+   * @param Store $store
+   */
+  public function __construct(Store $store)
+  {
+    $this->store = $store;
+    $this->useCache = $store->_getUseCache();
+    $this->cacheLifetime = $store->_getDefaultCacheLifetime();
+    $this->searchOptions = $store->_getSearchOptions();
+  }
+
+  /**
+   * Select specific fields
+   * @param array $fieldNames
+   * @return QueryBuilder
+   */
+  public function select(array $fieldNames): QueryBuilder
+  {
+    foreach ($fieldNames as $key => $fieldName) {
+      if(is_string($key)){
+        $this->fieldsToSelect[$key] = $fieldName;
+      } else {
+        $this->fieldsToSelect[] = $fieldName;
+      }
+    }
+    return $this;
+  }
+
+  /**
+   * Exclude specific fields
+   * @param string[] $fieldNames
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function except(array $fieldNames): QueryBuilder
+  {
+    $errorMsg = "If except is used an array containing strings with fieldNames has to be given";
+    foreach ($fieldNames as $fieldName) {
+      if (empty($fieldName)) {
+        continue;
+      }
+      if (!is_string($fieldName)) {
+        throw new InvalidArgumentException($errorMsg);
+      }
+      $this->fieldsToExclude[] = $fieldName;
+    }
+    return $this;
+  }
+
+  /**
+   * Add conditions to filter data.
+   * @param array $conditions
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function where(array $conditions): QueryBuilder
+  {
+    if (empty($conditions)) {
+      throw new InvalidArgumentException("You need to specify a where clause");
+    }
+
+    $this->whereConditions[] = $conditions;
+
+    return $this;
+  }
+
+  /**
+   * Add or-where conditions to filter data.
+   * @param array $conditions array(array(string fieldName, string condition, mixed value) [, array(...)])
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function orWhere(array $conditions): QueryBuilder
+  {
+
+    if (empty($conditions)) {
+      throw new InvalidArgumentException("You need to specify a where clause");
+    }
+
+    $this->whereConditions[] = "or";
+    $this->whereConditions[] = $conditions;
+
+    return $this;
+  }
+
+  /**
+   * Set the amount of data record to skip.
+   * @param int|string $skip
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function skip($skip = 0): QueryBuilder
+  {
+    if((!is_string($skip) || !is_numeric($skip)) && !is_int($skip)){
+      throw new InvalidArgumentException("Skip has to be an integer or a numeric string");
+    }
+
+    if(!is_int($skip)){
+      $skip = (int) $skip;
+    }
+
+    if($skip < 0){
+      throw new InvalidArgumentException("Skip has to be an integer >= 0");
+    }
+
+    $this->skip = $skip;
+
+    return $this;
+  }
+
+  /**
+   * Set the amount of data record to limit.
+   * @param int|string $limit
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function limit($limit = 0): QueryBuilder
+  {
+
+    if((!is_string($limit) || !is_numeric($limit)) && !is_int($limit)){
+      throw new InvalidArgumentException("Limit has to be an integer or a numeric string");
+    }
+
+    if(!is_int($limit)){
+      $limit = (int) $limit;
+    }
+
+    if($limit <= 0){
+      throw new InvalidArgumentException("Limit has to be an integer > 0");
+    }
+
+    $this->limit = $limit;
+
+    return $this;
+  }
+
+  /**
+   * Set the sort order.
+   * @param array $criteria to order by. array($fieldName => $order). $order can be "asc" or "desc"
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function orderBy( array $criteria): QueryBuilder
+  {
+    foreach ($criteria as $fieldName => $order){
+
+      if(!is_string($order)) {
+        throw new InvalidArgumentException('Order has to be a string! Please use "asc" or "desc" only.');
+      }
+
+      $order = strtolower($order);
+
+      if(!is_string($fieldName)) {
+        throw new InvalidArgumentException("Field name has to be a string");
+      }
+
+      if (!in_array($order, ['asc', 'desc'])) {
+        throw new InvalidArgumentException('Please use "asc" or "desc" only.');
+      }
+
+      $this->orderBy[] = [
+        'fieldName' => $fieldName,
+        'order' => $order
+      ];
+    }
+
+    return $this;
+  }
+
+  /**
+   * Do a fulltext like search against one or multiple fields.
+   * @param string|array $fields one or multiple fieldNames as an array
+   * @param string $query
+   * @param array $options
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function search($fields, string $query, array $options = []): QueryBuilder
+  {
+    if(!is_array($fields) && !is_string($fields)){
+      throw new InvalidArgumentException("Fields to search through have to be either a string or an array.");
+    }
+
+    if(!is_array($fields)){
+      $fields = (array)$fields;
+    }
+
+    if (empty($fields)) {
+      throw new InvalidArgumentException('Cant perform search due to no field name was provided');
+    }
+
+    if(count($fields) > 100){
+      trigger_error('Searching through more than 100 fields is not recommended and can be resource heavy.', E_USER_WARNING);
+    }
+
+    if (!empty($query)) {
+      $this->search = [
+        'fields' => $fields,
+        'query' => $query
+      ];
+      if(!empty($options)){
+        if(array_key_exists("minLength", $options) && is_int($options["minLength"]) && $options["minLength"] > 0){
+          $this->searchOptions["minLength"] = $options["minLength"];
+        }
+        if(array_key_exists("mode", $options) && is_string($options["mode"])){
+          $searchMode = strtolower(trim($options["mode"]));
+          if(in_array($searchMode, ["and", "or"])){
+            $this->searchOptions["mode"] = $searchMode;
+          }
+        }
+        if(array_key_exists("scoreKey", $options) && (is_string($options["scoreKey"]) || is_null($options["scoreKey"]))){
+          $this->searchOptions["scoreKey"] = $options["scoreKey"];
+        }
+        if(array_key_exists("algorithm", $options) && in_array($options["algorithm"], Query::SEARCH_ALGORITHM, true)){
+          $this->searchOptions["algorithm"] = $options["algorithm"];
+        }
+      }
+    }
+    return $this;
+  }
+
+  /**
+   * @param Closure $joinFunction
+   * @param string $propertyName
+   * @return QueryBuilder
+   */
+  public function join(Closure $joinFunction, string $propertyName): QueryBuilder
+  {
+    $this->listOfJoins[] = [
+      'propertyName' => $propertyName,
+      'joinFunction' => $joinFunction
+    ];
+    return $this;
+  }
+
+
+  /**
+   * Return distinct values.
+   * @param array|string $fields
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function distinct($fields = []): QueryBuilder
+  {
+    $fieldType = gettype($fields);
+    if ($fieldType === 'array') {
+      if ($fields === array_values($fields)) {
+        // Append fields.
+        $this->distinctFields = array_merge($this->distinctFields, $fields);
+      } else {
+        throw new InvalidArgumentException(
+          'Field value in distinct() method can not be an associative array, 
+          please provide a string or a list of string as a non-associative array.'
+        );
+      }
+    } else if ($fieldType === 'string' && !empty($fields)) {
+      $this->distinctFields[] = trim($fields);
+    } else {
+      throw new InvalidArgumentException(
+        'Field value in distinct() is invalid.'
+      );
+    }
+    return $this;
+  }
+
+  /**
+   * Use caching for current query
+   * @param null|int $lifetime time to live as int in seconds or null to regenerate cache on every insert, update and delete
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function useCache(int $lifetime = null): QueryBuilder
+  {
+    $this->useCache = true;
+    if((!is_int($lifetime) || $lifetime < 0) && !is_null($lifetime)){
+      throw new InvalidArgumentException("lifetime has to be int >= 0 or null");
+    }
+    $this->cacheLifetime = $lifetime;
+    return $this;
+  }
+
+  /**
+   * Disable cache for the query.
+   * @return QueryBuilder
+   */
+  public function disableCache(): QueryBuilder
+  {
+    $this->useCache = false;
+    return $this;
+  }
+
+  /**
+   * Re-generate the cache for the query.
+   * @return QueryBuilder
+   */
+  public function regenerateCache(): QueryBuilder
+  {
+    $this->regenerateCache = true;
+    return $this;
+  }
+
+  /**
+   * @return Query
+   */
+  public function getQuery(): Query
+  {
+    return new Query($this);
+  }
+
+  /**
+   * @param array $groupByFields
+   * @param string|null $countKeyName
+   * @param bool $allowEmpty
+   * @return QueryBuilder
+   */
+  public function groupBy(array $groupByFields, string $countKeyName = null, bool $allowEmpty = false): QueryBuilder
+  {
+    $this->groupBy = [
+      "groupByFields" => $groupByFields,
+      "countKeyName" => $countKeyName,
+      "allowEmpty" => $allowEmpty
+    ];
+    return $this;
+  }
+
+  /**
+   * Filter result data of groupBy
+   * @param array $criteria
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   */
+  public function having(array $criteria): QueryBuilder
+  {
+    if (empty($criteria)) {
+      throw new InvalidArgumentException("You need to specify a having clause");
+    }
+    $this->havingConditions = $criteria;
+    return $this;
+  }
+
+  /**
+   * Returns a an array used to generate a unique token for the current query.
+   * @return array
+   */
+  public function _getCacheTokenArray(): array
+  {
+    $properties = [];
+    $conditionsArray = $this->_getConditionProperties();
+
+    foreach ($conditionsArray as $propertyName => $propertyValue){
+      if(!in_array($propertyName, $this->propertiesNotUsedForCacheToken, true)){
+        $properties[$propertyName] = $propertyValue;
+      }
+    }
+
+    return $properties;
+  }
+
+  /**
+   * Returns an array containing all information needed to execute an query.
+   * @return array
+   */
+  public function _getConditionProperties(): array
+  {
+    $allProperties = get_object_vars($this);
+    $properties = [];
+
+    foreach ($allProperties as $propertyName => $propertyValue){
+      if(!in_array($propertyName, $this->propertiesNotUsedInConditionsArray, true)){
+        $properties[$propertyName] = $propertyValue;
+      }
+    }
+
+    return $properties;
+  }
+
+  /**
+   * Returns the Store object used to create the QueryBuilder object.
+   * @return Store
+   */
+  public function _getStore(): Store{
+      return $this->store;
+  }
+
+  /**
+   * Add "in" condition to filter data.
+   * @param string $fieldName
+   * @param array $values
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   * @deprecated since version 2.4, use where and orWhere instead.
+   */
+  public function in(string $fieldName, array $values = []): QueryBuilder
+  {
+    if (empty($fieldName)) {
+      throw new InvalidArgumentException('Field name for in clause can not be empty.');
+    }
+
+    // Add to conditions with "AND" operation
+    $this->whereConditions[] = [$fieldName, "in", $values];
+    return $this;
+  }
+
+  /**
+   * Add "not in" condition to filter data.
+   * @param string $fieldName
+   * @param array $values
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   * @deprecated since version 2.4, use where and orWhere instead.
+   */
+  public function notIn(string $fieldName, array $values = []): QueryBuilder
+  {
+    if (empty($fieldName)) {
+      throw new InvalidArgumentException('Field name for notIn clause can not be empty.');
+    }
+
+    // Add to conditions with "AND" operation
+    $this->whereConditions[] = [$fieldName, "not in", $values];
+    return $this;
+  }
+
+  /**
+   * Add a where statement that is nested. ( $x or ($y and $z) )
+   * @param array $conditions
+   * @return QueryBuilder
+   * @throws InvalidArgumentException
+   * @deprecated since version 2.3, use where or orWhere instead.
+   */
+  public function nestedWhere(array $conditions): QueryBuilder
+  {
+    // TODO remove with version 3.0
+    if(empty($conditions)){
+      throw new InvalidArgumentException("You need to specify nested where clauses");
+    }
+
+    if(count($conditions) > 1){
+      throw new InvalidArgumentException("You are not allowed to specify multiple elements at the first depth!");
+    }
+
+    $outerMostOperation = (array_keys($conditions))[0];
+    $outerMostOperation = (is_string($outerMostOperation)) ? strtolower($outerMostOperation) : $outerMostOperation;
+
+    $allowedOuterMostOperations = [0, "and", "or"];
+
+    if(!in_array($outerMostOperation, $allowedOuterMostOperations, true)){
+      throw new InvalidArgumentException("Outer most operation has to one of the following: ( 0 / and / or ) ");
+    }
+
+    $this->nestedWhere = $conditions;
+
+    return $this;
+  }
+
+}
diff --git a/core/class/sleekDB/SleekDB.php b/core/class/sleekDB/SleekDB.php
new file mode 100644
index 00000000..76ef66eb
--- /dev/null
+++ b/core/class/sleekDB/SleekDB.php
@@ -0,0 +1,578 @@
+<?php
+
+namespace SleekDB;
+
+use Closure;
+use SleekDB\Exceptions\InvalidArgumentException;
+use SleekDB\Exceptions\IdNotAllowedException;
+use SleekDB\Exceptions\InvalidConfigurationException;
+use SleekDB\Exceptions\IOException;
+use SleekDB\Exceptions\JsonException;
+
+if(false === class_exists("\Composer\Autoload\ClassLoader")){
+    require_once __DIR__.'/Store.php';
+}
+
+/**
+ * Class SleekDB
+ * @package SleekDB
+ * @deprecated since version 2.0, use SleekDB\Store instead.
+ */
+class SleekDB
+{
+
+  /**
+   * @var QueryBuilder
+   */
+  protected $queryBuilder;
+
+  /**
+   * @var Store
+   */
+  protected $store;
+
+  private $shouldKeepConditions = false;
+
+  /**
+   * SleekDB constructor.
+   * @param string $storeName
+   * @param string $dataDir
+   * @param array $configuration
+   * @throws InvalidArgumentException
+   * @throws IOException
+   * @throws InvalidConfigurationException
+   */
+  public function __construct(string $storeName, string $dataDir, array $configuration = []){
+    $this->init($storeName, $dataDir, $configuration);
+  }
+
+  /**
+   * Initialize the SleekDB instance.
+   * @param string $storeName
+   * @param string $dataDir
+   * @param array $conf
+   * @throws InvalidArgumentException
+   * @throws IOException
+   * @throws InvalidConfigurationException
+   */
+  public function init(string $storeName, string $dataDir, array $conf = []){
+    $this->setStore(new Store($storeName, $dataDir, $conf));
+    $this->setQueryBuilder($this->getStore()->createQueryBuilder());
+  }
+
+  /**
+   * Initialize the store.
+   * @param string $storeName
+   * @param string $dataDir
+   * @param array $configuration
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   * @throws IOException
+   * @throws InvalidConfigurationException
+   */
+  public static function store(string $storeName, string $dataDir, array $configuration = []): SleekDB
+  {
+    return new SleekDB($storeName, $dataDir, $configuration);
+  }
+
+  /**
+   * Execute Query and get Results
+   * @return array
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function fetch(): array
+  {
+    return $this->getQuery()->fetch();
+  }
+
+  /**
+   * Check if data is found
+   * @return bool
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function exists(): bool
+  {
+    return $this->getQuery()->exists();
+  }
+
+  /**
+   * Return the first document.
+   * @return array
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function first(): array
+  {
+    return $this->getQuery()->first();
+  }
+
+  /**
+   * Creates a new object in the store.
+   * It is stored as a plaintext JSON document.
+   * @param array $storeData
+   * @return array
+   * @throws IOException
+   * @throws IdNotAllowedException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function insert(array $storeData): array
+  {
+    return $this->getStore()->insert($storeData);
+  }
+
+  /**
+   * Creates multiple objects in the store.
+   * @param array $storeData
+   * @return array
+   * @throws IOException
+   * @throws IdNotAllowedException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function insertMany(array $storeData): array
+  {
+    return $this->getStore()->insertMany($storeData);
+  }
+
+  /**
+   * Update one or multiple documents, based on current query
+   * @param array $updatable
+   * @return bool
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function update(array $updatable): bool
+  {
+    return $this->getQuery()->update($updatable);
+  }
+
+  /**
+   * Deletes matched store objects.
+   * @param int $returnOption
+   * @return bool|array|int
+   * @throws InvalidArgumentException
+   * @throws IOException
+   */
+  public function delete(int $returnOption = Query::DELETE_RETURN_BOOL){
+    return $this->getQuery()->delete($returnOption);
+  }
+
+  /**
+   * Deletes a store and wipes all the data and cache it contains.
+   * @return bool
+   * @throws IOException
+   */
+  public function deleteStore(): bool
+  {
+    return $this->getStore()->deleteStore();
+  }
+
+  /**
+   * This method would make a unique token for the current query.
+   * We would use this hash token as the id/name of the cache file.
+   * @return string
+   */
+  public function getCacheToken(): string
+  {
+    return $this->getQueryBuilder()->getQuery()->getCache()->getToken();
+  }
+
+  /**
+   * Select specific fields
+   * @param string[] $fieldNames
+   * @return SleekDB
+   */
+  public function select(array $fieldNames): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->select($fieldNames));
+    return $this;
+  }
+
+  /**
+   * Exclude specific fields
+   * @param string[] $fieldNames
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function except(array $fieldNames): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->except($fieldNames));
+    return $this;
+  }
+
+  /**
+   * Add conditions to filter data.
+   * @param string|array|mixed ...$conditions (string fieldName, string condition, mixed value) OR (array(array(string fieldName, string condition, mixed value)[, array(...)]))
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function where(...$conditions): SleekDB
+  {
+    foreach ($conditions as $key => $arg) {
+      if ($key > 0) {
+        throw new InvalidArgumentException("Allowed: (string fieldName, string condition, mixed value) OR (array(array(string fieldName, string condition, mixed value)[, array(...)]))");
+      }
+      if (is_array($arg)) {
+        // parameters given as arrays for multiple "where" with "and" between each condition
+        $this->setQueryBuilder($this->getQueryBuilder()->where($arg));
+        break;
+      }
+      if (count($conditions) === 3) {
+        // parameters given as (string fieldName, string condition, mixed value) for a single "where"
+        $this->setQueryBuilder($this->getQueryBuilder()->where($conditions));
+        break;
+      }
+    }
+
+    return $this;
+  }
+
+  /**
+   * Add "in" condition to filter data.
+   * @param string $fieldName
+   * @param array $values
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function in(string $fieldName, array $values = []): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->in($fieldName, $values));
+    return $this;
+  }
+
+  /**
+   * Add "not in" condition to filter data.
+   * @param string $fieldName
+   * @param array $values
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function notIn(string $fieldName, array $values = []): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->notIn($fieldName, $values));
+    return $this;
+  }
+
+  /**
+   * Add or-where conditions to filter data.
+   * @param string|array|mixed ...$conditions (string fieldName, string condition, mixed value) OR array(array(string fieldName, string condition, mixed value) [, array(...)])
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function orWhere(...$conditions): SleekDB
+  {
+    foreach ($conditions as $key => $arg) {
+      if ($key > 0) {
+        throw new InvalidArgumentException("Allowed: (string fieldName, string condition, mixed value) OR array(array(string fieldName, string condition, mixed value) [, array(...)])");
+      }
+      if (is_array($arg)) {
+        // parameters given as arrays for an "or where" with "and" between each condition
+        $this->setQueryBuilder($this->getQueryBuilder()->orWhere($arg));
+        break;
+      }
+      if (count($conditions) === 3) {
+        // parameters given as (string fieldName, string condition, mixed value) for a single "or where"
+        $this->setQueryBuilder($this->getQueryBuilder()->orWhere($conditions));
+        break;
+      }
+    }
+
+    return $this;
+  }
+
+  /**
+   * Set the amount of data record to skip.
+   * @param int $skip
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function skip(int $skip = 0): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->skip($skip));
+    return $this;
+  }
+
+  /**
+   * Set the amount of data record to limit.
+   * @param int $limit
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function limit(int $limit = 0): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->limit($limit));
+    return $this;
+  }
+
+  /**
+   * Set the sort order.
+   * @param string $order "asc" or "desc"
+   * @param string $orderBy
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function orderBy(string $order, string $orderBy = '_id'): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->orderBy([$orderBy => $order]));
+    return $this;
+  }
+
+  /**
+   * Do a fulltext like search against more than one field.
+   * @param string|array $field one fieldName or multiple fieldNames as an array
+   * @param string $keyword
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function search($field, string $keyword): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->search($field, $keyword));
+    return $this;
+  }
+
+  /**
+   * @param Closure $joinedStore
+   * @param string $dataPropertyName
+   * @return SleekDB
+   */
+  public function join(Closure $joinedStore, string $dataPropertyName): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->join($joinedStore, $dataPropertyName));
+    return $this;
+  }
+
+  /**
+   * Re-generate the cache for the query.
+   * @return SleekDB
+   */
+  public function makeCache(): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->regenerateCache());
+    return $this;
+  }
+
+  /**
+   * Disable cache for the query.
+   * @return SleekDB
+   */
+  public function disableCache(): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->disableCache());
+    return $this;
+  }
+
+  /**
+   * Use caching for current query
+   * @param int|null $lifetime time to live as int in seconds or null to regenerate cache on every insert, update and delete
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function useCache(int $lifetime = null): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->useCache($lifetime));
+    return $this;
+  }
+
+  /**
+   * Delete cache file/s for current query.
+   * @return SleekDB
+   */
+  public function deleteCache(): SleekDB
+  {
+    $this->getQueryBuilder()->getQuery()->getCache()->delete();
+    return $this;
+  }
+
+  /**
+   * Delete all cache files for current store.
+   * @return SleekDB
+   */
+  public function deleteAllCache(): SleekDB
+  {
+    $this->getQueryBuilder()->getQuery()->getCache()->deleteAll();
+    return $this;
+  }
+
+  /**
+   * Keep the active query conditions.
+   * @return SleekDB
+   */
+  public function keepConditions(): SleekDB
+  {
+    $this->shouldKeepConditions = true;
+    return $this;
+  }
+
+  /**
+   * Return distinct values.
+   * @param array|string $fields
+   * @return SleekDB
+   * @throws InvalidArgumentException
+   */
+  public function distinct($fields = []): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->distinct($fields));
+    return $this;
+  }
+
+  /**
+   * @return QueryBuilder
+   */
+  public function getQueryBuilder(): QueryBuilder
+  {
+    return $this->queryBuilder;
+  }
+
+  /**
+   * @param QueryBuilder $queryBuilder
+   */
+  private function setQueryBuilder(QueryBuilder $queryBuilder){
+      $this->queryBuilder = $queryBuilder;
+  }
+
+  /**
+   * @return Query
+   */
+  public function getQuery(): Query
+  {
+    $query = $this->getQueryBuilder()->getQuery();
+    $this->resetQueryBuilder();
+    return $query;
+  }
+
+  /**
+   * @return Cache
+   */
+  public function getCache(): Cache
+  {
+    // we do not want to reset the QueryBuilder
+    return $this->getQueryBuilder()->getQuery()->getCache();
+  }
+
+
+  /**
+   * @param Store $store
+   */
+  private function setStore(Store $store){
+      $this->store = $store;
+  }
+
+  /**
+   * @return Store
+   */
+  public function getStore(): Store
+  {
+    return $this->store;
+  }
+
+  /**
+   * Handle shouldKeepConditions and reset queryBuilder accordingly
+   */
+  private function resetQueryBuilder(){
+    if($this->shouldKeepConditions === true) {
+      return;
+    }
+    $this->setQueryBuilder($this->getStore()->createQueryBuilder());
+  }
+
+
+  /**
+   * Retrieve all documents.
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findAll(): array
+  {
+    return $this->getStore()->findAll();
+  }
+
+  /**
+   * Retrieve one document by its _id. Very fast because it finds the document by its file path.
+   * @param int $id
+   * @return array|null
+   * @throws InvalidArgumentException
+   */
+  public function findById(int $id){
+    return $this->getStore()->findById($id);
+  }
+
+  /**
+   * Retrieve one or multiple documents.
+   * @param array $criteria
+   * @param array $orderBy
+   * @param int $limit
+   * @param int $offset
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findBy(array $criteria, array $orderBy = null, int $limit = null, int $offset = null): array
+  {
+    return $this->getStore()->findBy($criteria, $orderBy, $limit, $offset);
+  }
+
+  /**
+   * Retrieve one document.
+   * @param array $criteria
+   * @return array|null single document or NULL if no document can be found
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findOneBy(array $criteria)
+  {
+    return $this->getStore()->findOneBy($criteria);
+  }
+
+  /**
+   * Update one or multiple documents.
+   * @param array $updatable true if all documents could be updated and false if one document did not exist
+   * @return bool
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function updateBy(array $updatable): bool
+  {
+    return $this->getStore()->update($updatable);
+  }
+
+  /**
+   * Delete one or multiple documents.
+   * @param $criteria
+   * @param int $returnOption
+   * @return array|bool|int
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function deleteBy($criteria, $returnOption = Query::DELETE_RETURN_BOOL){
+    return $this->getStore()->deleteBy($criteria, $returnOption);
+  }
+
+  /**
+   * Delete one document by its _id. Very fast because it deletes the document by its file path.
+   * @param $id
+   * @return bool true if document does not exist or deletion was successful, false otherwise
+   * @throws IOException
+   */
+  public function deleteById($id): bool
+  {
+    return $this->getStore()->deleteById($id);
+  }
+
+  /**
+   * Add a where statement that is nested. ( $x or ($y and $z) )
+   * @param array $conditions
+   * @return $this
+   * @throws InvalidArgumentException
+   * @deprecated since version 2.3, use where and orWhere instead.
+   */
+  public function nestedWhere(array $conditions): SleekDB
+  {
+    $this->setQueryBuilder($this->getQueryBuilder()->nestedWhere($conditions));
+    return $this;
+  }
+
+}
diff --git a/core/class/sleekDB/Store.php b/core/class/sleekDB/Store.php
new file mode 100644
index 00000000..9ce2492c
--- /dev/null
+++ b/core/class/sleekDB/Store.php
@@ -0,0 +1,888 @@
+<?php
+
+namespace SleekDB;
+
+use Exception;
+use SleekDB\Classes\IoHelper;
+use SleekDB\Classes\NestedHelper;
+use SleekDB\Exceptions\InvalidArgumentException;
+use SleekDB\Exceptions\IdNotAllowedException;
+use SleekDB\Exceptions\InvalidConfigurationException;
+use SleekDB\Exceptions\IOException;
+use SleekDB\Exceptions\JsonException;
+
+// To provide usage without composer, we need to require all files.
+if(false === class_exists("\Composer\Autoload\ClassLoader")) {
+    foreach (glob(__DIR__ . '/Exceptions/*.php') as $exception) {
+        require_once $exception;
+    }
+    foreach (glob(__DIR__ . '/Classes/*.php') as $traits) {
+      require_once $traits;
+    }
+    foreach (glob(__DIR__ . '/*.php') as $class) {
+        if (strpos($class, 'SleekDB.php') !== false || strpos($class, 'Store.php') !== false) {
+          continue;
+        }
+        require_once $class;
+    }
+}
+
+class Store
+{
+
+  protected $root = __DIR__;
+
+  protected $storeName = "";
+  protected $storePath = "";
+
+  protected $databasePath = "";
+
+  protected $useCache = true;
+  protected $defaultCacheLifetime;
+  protected $primaryKey = "_id";
+  protected $timeout = 120;
+  protected $searchOptions = [
+    "minLength" => 2,
+    "scoreKey" => "searchScore",
+    "mode" => "or",
+    "algorithm" => Query::SEARCH_ALGORITHM["hits"]
+  ];
+
+  const dataDirectory = "data/";
+
+  /**
+   * Store constructor.
+   * @param string $storeName
+   * @param string $databasePath
+   * @param array $configuration
+   * @throws InvalidArgumentException
+   * @throws IOException
+   * @throws InvalidConfigurationException
+   */
+  public function __construct(string $storeName, string $databasePath, array $configuration = [])
+  {
+    $storeName = trim($storeName);
+    if (empty($storeName)) {
+      throw new InvalidArgumentException('store name can not be empty');
+    }
+    $this->storeName = $storeName;
+
+    $databasePath = trim($databasePath);
+    if (empty($databasePath)) {
+      throw new InvalidArgumentException('data directory can not be empty');
+    }
+
+    IoHelper::normalizeDirectory($databasePath);
+    $this->databasePath = $databasePath;
+
+    $this->setConfiguration($configuration);
+
+    // boot store
+    $this->createDatabasePath();
+    $this->createStore();
+  }
+
+  /**
+   * Change the destination of the store object.
+   * @param string $storeName
+   * @param string|null $databasePath If empty, previous database path will be used.
+   * @param array $configuration
+   * @return Store
+   * @throws IOException
+   * @throws InvalidArgumentException
+   * @throws InvalidConfigurationException
+   */
+  public function changeStore(string $storeName, string $databasePath = null, array $configuration = []): Store
+  {
+    if(empty($databasePath)){
+      $databasePath = $this->getDatabasePath();
+    }
+    $this->__construct($storeName, $databasePath, $configuration);
+    return $this;
+  }
+
+  /**
+   * @return string
+   */
+  public function getStoreName(): string
+  {
+    return $this->storeName;
+  }
+
+  /**
+   * @return string
+   */
+  public function getDatabasePath(): string
+  {
+    return $this->databasePath;
+  }
+
+  /**
+   * @return QueryBuilder
+   */
+  public function createQueryBuilder(): QueryBuilder
+  {
+    return new QueryBuilder($this);
+  }
+
+  /**
+   * Insert a new document to the store.
+   * It is stored as a plaintext JSON document.
+   * @param array $data
+   * @return array inserted document
+   * @throws IOException
+   * @throws IdNotAllowedException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function insert(array $data): array
+  {
+    // Handle invalid data
+    if (empty($data)) {
+      throw new InvalidArgumentException('No data found to insert in the store');
+    }
+
+    $data = $this->writeNewDocumentToStore($data);
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return $data;
+  }
+
+  /**
+   * Insert multiple documents to the store.
+   * They are stored as plaintext JSON documents.
+   * @param array $data
+   * @return array inserted documents
+   * @throws IOException
+   * @throws IdNotAllowedException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function insertMany(array $data): array
+  {
+    // Handle invalid data
+    if (empty($data)) {
+      throw new InvalidArgumentException('No data found to insert in the store');
+    }
+
+    // All results.
+    $results = [];
+    foreach ($data as $document) {
+      $results[] = $this->writeNewDocumentToStore($document);
+    }
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+    return $results;
+  }
+
+
+  /**
+   * Delete store with all its data and cache.
+   * @return bool
+   * @throws IOException
+   */
+  public function deleteStore(): bool
+  {
+    $storePath = $this->getStorePath();
+    return IoHelper::deleteFolder($storePath);
+  }
+
+
+  /**
+   * Return the last created store object ID.
+   * @return int
+   * @throws IOException
+   */
+  public function getLastInsertedId(): int
+  {
+    $counterPath = $this->getStorePath() . '_cnt.sdb';
+
+    return (int) IoHelper::getFileContent($counterPath);
+  }
+
+  /**
+   * @return string
+   */
+  public function getStorePath(): string
+  {
+    return $this->storePath;
+  }
+
+  /**
+   * Retrieve all documents.
+   * @param array|null $orderBy array($fieldName => $order). $order can be "asc" or "desc"
+   * @param int|null $limit the amount of data record to limit
+   * @param int|null $offset the amount of data record to skip
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findAll(array $orderBy = null, int $limit = null, int $offset = null): array
+  {
+    $qb = $this->createQueryBuilder();
+    if(!is_null($orderBy)){
+      $qb->orderBy($orderBy);
+    }
+    if(!is_null($limit)){
+      $qb->limit($limit);
+    }
+    if(!is_null($offset)){
+      $qb->skip($offset);
+    }
+    return $qb->getQuery()->fetch();
+  }
+
+  /**
+   * Retrieve one document by its primary key. Very fast because it finds the document by its file path.
+   * @param int|string $id
+   * @return array|null
+   * @throws InvalidArgumentException
+   */
+  public function findById($id){
+
+    $id = $this->checkAndStripId($id);
+
+    $filePath = $this->getDataPath() . "$id.json";
+
+    try{
+      $content = IoHelper::getFileContent($filePath);
+    } catch (Exception $exception){
+      return null;
+    }
+
+    return @json_decode($content, true);
+  }
+
+  /**
+   * Retrieve one or multiple documents.
+   * @param array $criteria
+   * @param array $orderBy
+   * @param int $limit
+   * @param int $offset
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findBy(array $criteria, array $orderBy = null, int $limit = null, int $offset = null): array
+  {
+    $qb = $this->createQueryBuilder();
+
+    $qb->where($criteria);
+
+    if($orderBy !== null) {
+      $qb->orderBy($orderBy);
+    }
+    if($limit !== null) {
+      $qb->limit($limit);
+    }
+    if($offset !== null) {
+      $qb->skip($offset);
+    }
+
+    return $qb->getQuery()->fetch();
+  }
+
+  /**
+   * Retrieve one document.
+   * @param array $criteria
+   * @return array|null single document or NULL if no document can be found
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function findOneBy(array $criteria)
+  {
+    $qb = $this->createQueryBuilder();
+
+    $qb->where($criteria);
+
+    $result = $qb->getQuery()->first();
+
+    return (!empty($result))? $result : null;
+
+  }
+
+  /**
+   * Update or insert one document.
+   * @param array $data
+   * @param bool $autoGenerateIdOnInsert
+   * @return array updated / inserted document
+   * @throws IOException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function updateOrInsert(array $data, bool $autoGenerateIdOnInsert = true): array
+  {
+    $primaryKey = $this->getPrimaryKey();
+
+    if(empty($data)) {
+      throw new InvalidArgumentException("No document to update or insert.");
+    }
+
+//    // we can use this check to determine if multiple documents are given
+//    // because documents have to have at least the primary key.
+//    if(array_keys($data) !== range(0, (count($data) - 1))){
+//      $data = [ $data ];
+//    }
+
+    if(!array_key_exists($primaryKey, $data)) {
+//        $documentString = var_export($document, true);
+//        throw new InvalidArgumentException("Documents have to have the primary key \"$primaryKey\". Got data: $documentString");
+      $data[$primaryKey] = $this->increaseCounterAndGetNextId();
+    } else {
+      $data[$primaryKey] = $this->checkAndStripId($data[$primaryKey]);
+      if($autoGenerateIdOnInsert && $this->findById($data[$primaryKey]) === null){
+        $data[$primaryKey] = $this->increaseCounterAndGetNextId();
+      }
+    }
+
+    // One document to update or insert
+
+    // save to access file with primary key value because we secured it above
+    $storePath = $this->getDataPath() . "$data[$primaryKey].json";
+    IoHelper::writeContentToFile($storePath, json_encode($data));
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return $data;
+  }
+
+  /**
+   * Update or insert multiple documents.
+   * @param array $data
+   * @param bool $autoGenerateIdOnInsert
+   * @return array updated / inserted documents
+   * @throws IOException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function updateOrInsertMany(array $data, bool $autoGenerateIdOnInsert = true): array
+  {
+    $primaryKey = $this->getPrimaryKey();
+
+    if(empty($data)) {
+      throw new InvalidArgumentException("No documents to update or insert.");
+    }
+
+//    // we can use this check to determine if multiple documents are given
+//    // because documents have to have at least the primary key.
+//    if(array_keys($data) !== range(0, (count($data) - 1))){
+//      $data = [ $data ];
+//    }
+
+    // Check if all documents have the primary key before updating or inserting any
+    foreach ($data as $key => $document){
+      if(!is_array($document)) {
+        throw new InvalidArgumentException('Documents have to be an arrays.');
+      }
+      if(!array_key_exists($primaryKey, $document)) {
+//        $documentString = var_export($document, true);
+//        throw new InvalidArgumentException("Documents have to have the primary key \"$primaryKey\". Got data: $documentString");
+        $document[$primaryKey] = $this->increaseCounterAndGetNextId();
+      } else {
+        $document[$primaryKey] = $this->checkAndStripId($document[$primaryKey]);
+        if($autoGenerateIdOnInsert && $this->findById($document[$primaryKey]) === null){
+          $document[$primaryKey] = $this->increaseCounterAndGetNextId();
+        }
+      }
+      // after the stripping and checking we apply it back
+      $data[$key] = $document;
+    }
+
+    // One or multiple documents to update or insert
+    foreach ($data as $document) {
+      // save to access file with primary key value because we secured it above
+      $storePath = $this->getDataPath() . "$document[$primaryKey].json";
+      IoHelper::writeContentToFile($storePath, json_encode($document));
+    }
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return $data;
+  }
+
+
+  /**
+   * Update one or multiple documents.
+   * @param array $updatable
+   * @return bool true if all documents could be updated and false if one document did not exist
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function update(array $updatable): bool
+  {
+    $primaryKey = $this->getPrimaryKey();
+
+    if(empty($updatable)) {
+      throw new InvalidArgumentException("No documents to update.");
+    }
+
+    // we can use this check to determine if multiple documents are given
+    // because documents have to have at least the primary key.
+    if(array_keys($updatable) !== range(0, (count($updatable) - 1))){
+      $updatable = [ $updatable ];
+    }
+
+    // Check if all documents exist and have the primary key before updating any
+    foreach ($updatable as $key => $document){
+      if(!is_array($document)) {
+        throw new InvalidArgumentException('Documents have to be an arrays.');
+      }
+      if(!array_key_exists($primaryKey, $document)) {
+        throw new InvalidArgumentException("Documents have to have the primary key \"$primaryKey\".");
+      }
+
+      $document[$primaryKey] = $this->checkAndStripId($document[$primaryKey]);
+      // after the stripping and checking we apply it back to the updatable array.
+      $updatable[$key] = $document;
+
+      $storePath = $this->getDataPath() . "$document[$primaryKey].json";
+
+      if (!file_exists($storePath)) {
+        return false;
+      }
+    }
+
+    // One or multiple documents to update
+    foreach ($updatable as $document) {
+      // save to access file with primary key value because we secured it above
+      $storePath = $this->getDataPath() . "$document[$primaryKey].json";
+      IoHelper::writeContentToFile($storePath, json_encode($document));
+    }
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return true;
+  }
+
+  /**
+   * Update properties of one document.
+   * @param int|string $id
+   * @param array $updatable
+   * @return array|false Updated document or false if document does not exist.
+   * @throws IOException If document could not be read or written.
+   * @throws InvalidArgumentException If one key to update is primary key or $id is not int or string.
+   * @throws JsonException If content of document file could not be decoded.
+   */
+  public function updateById($id, array $updatable)
+  {
+
+    $id = $this->checkAndStripId($id);
+
+    $filePath = $this->getDataPath() . "$id.json";
+
+    $primaryKey = $this->getPrimaryKey();
+
+    if(array_key_exists($primaryKey, $updatable)) {
+      throw new InvalidArgumentException("You can not update the primary key \"$primaryKey\" of documents.");
+    }
+
+    if(!file_exists($filePath)){
+      return false;
+    }
+
+    $content = IoHelper::updateFileContent($filePath, function($content) use ($filePath, $updatable){
+      $content = @json_decode($content, true);
+      if(!is_array($content)){
+        throw new JsonException("Could not decode content of \"$filePath\" with json_decode.");
+      }
+      foreach ($updatable as $key => $value){
+        NestedHelper::updateNestedValue($key, $content, $value);
+      }
+      return json_encode($content);
+    });
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return json_decode($content, true);
+  }
+
+  /**
+   * Delete one or multiple documents.
+   * @param array $criteria
+   * @param int $returnOption
+   * @return array|bool|int
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function deleteBy(array $criteria, int $returnOption = Query::DELETE_RETURN_BOOL){
+
+    $query = $this->createQueryBuilder()->where($criteria)->getQuery();
+
+    $query->getCache()->deleteAllWithNoLifetime();
+
+    return $query->delete($returnOption);
+  }
+
+  /**
+   * Delete one document by its primary key. Very fast because it deletes the document by its file path.
+   * @param int|string $id
+   * @return bool true if document does not exist or deletion was successful, false otherwise
+   * @throws InvalidArgumentException
+   */
+  public function deleteById($id): bool
+  {
+
+    $id = $this->checkAndStripId($id);
+
+    $filePath = $this->getDataPath() . "$id.json";
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return (!file_exists($filePath) || true === @unlink($filePath));
+  }
+
+  /**
+   * Remove fields from one document by its primary key.
+   * @param int|string $id
+   * @param array $fieldsToRemove
+   * @return false|array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   * @throws JsonException
+   */
+  public function removeFieldsById($id, array $fieldsToRemove)
+  {
+    $id = $this->checkAndStripId($id);
+    $filePath = $this->getDataPath() . "$id.json";
+    $primaryKey = $this->getPrimaryKey();
+
+    if(in_array($primaryKey, $fieldsToRemove, false)) {
+      throw new InvalidArgumentException("You can not remove the primary key \"$primaryKey\" of documents.");
+    }
+    if(!file_exists($filePath)){
+      return false;
+    }
+
+    $content = IoHelper::updateFileContent($filePath, function($content) use ($filePath, $fieldsToRemove){
+      $content = @json_decode($content, true);
+      if(!is_array($content)){
+        throw new JsonException("Could not decode content of \"$filePath\" with json_decode.");
+      }
+      foreach ($fieldsToRemove as $fieldToRemove){
+        NestedHelper::removeNestedField($content, $fieldToRemove);
+      }
+      return $content;
+    });
+
+    $this->createQueryBuilder()->getQuery()->getCache()->deleteAllWithNoLifetime();
+
+    return json_decode($content, true);
+  }
+
+  /**
+   * Do a fulltext like search against one or multiple fields.
+   * @param array $fields
+   * @param string $query
+   * @param array|null $orderBy
+   * @param int|null $limit
+   * @param int|null $offset
+   * @return array
+   * @throws IOException
+   * @throws InvalidArgumentException
+   */
+  public function search(array $fields, string $query, array $orderBy = null, int $limit = null, int $offset = null): array
+  {
+
+    $qb = $this->createQueryBuilder();
+
+    $qb->search($fields, $query);
+
+    if($orderBy !== null) {
+      $qb->orderBy($orderBy);
+    }
+
+    if($limit !== null) {
+      $qb->limit($limit);
+    }
+
+    if($offset !== null) {
+      $qb->skip($offset);
+    }
+
+    return $qb->getQuery()->fetch();
+  }
+
+  /**
+   * Get the name of the field used as the primary key.
+   * @return string
+   */
+  public function getPrimaryKey(): string
+  {
+    return $this->primaryKey;
+  }
+
+  /**
+   * Returns the amount of documents in the store.
+   * @return int
+   * @throws IOException
+   */
+  public function count(): int
+  {
+    if($this->_getUseCache() === true){
+      $cacheTokenArray = ["count" => true];
+      $cache = new Cache($this->getStorePath(), $cacheTokenArray, null);
+      $cacheValue = $cache->get();
+      if(is_array($cacheValue) && array_key_exists("count", $cacheValue)){
+        return $cacheValue["count"];
+      }
+    }
+    $value = [
+      "count" => IoHelper::countFolderContent($this->getDataPath())
+    ];
+    if(isset($cache)) {
+      $cache->set($value);
+    }
+    return $value["count"];
+  }
+
+  /**
+   * Returns the search options of the store.
+   * @return array
+   */
+  public function _getSearchOptions(): array
+  {
+    return $this->searchOptions;
+  }
+
+  /**
+   * Returns if caching is enabled store wide.
+   * @return bool
+   */
+  public function _getUseCache(): bool
+  {
+    return $this->useCache;
+  }
+
+  /**
+   * Returns the store wide default cache lifetime.
+   * @return null|int
+   */
+  public function _getDefaultCacheLifetime()
+  {
+    return $this->defaultCacheLifetime;
+  }
+
+  /**
+   * @return string
+   * @deprecated since version 2.7, use getDatabasePath instead.
+   */
+  public function getDataDirectory(): string
+  {
+    // TODO remove with version 3.0
+    return $this->databasePath;
+  }
+
+  /**
+   * @throws IOException
+   */
+  private function createDatabasePath()
+  {
+    $databasePath = $this->getDatabasePath();
+    IoHelper::createFolder($databasePath);
+  }
+
+  /**
+   * @throws IOException
+   */
+  private function createStore()
+  {
+    $storeName = $this->getStoreName();
+    // Prepare store name.
+    IoHelper::normalizeDirectory($storeName);
+    // Store directory path.
+    $this->storePath = $this->getDatabasePath() . $storeName;
+    $storePath = $this->getStorePath();
+    IoHelper::createFolder($storePath);
+
+    // Create the cache directory.
+    $cacheDirectory = $storePath . 'cache';
+    IoHelper::createFolder($cacheDirectory);
+
+    // Create the data directory.
+    IoHelper::createFolder($storePath . self::dataDirectory);
+
+    // Create the store counter file.
+    $counterFile = $storePath . '_cnt.sdb';
+    if(!file_exists($counterFile)){
+      IoHelper::writeContentToFile($counterFile, '0');
+    }
+  }
+
+  /**
+   * @param array $configuration
+   * @throws InvalidConfigurationException
+   */
+  private function setConfiguration(array $configuration)
+  {
+    if(array_key_exists("auto_cache", $configuration)){
+      $autoCache = $configuration["auto_cache"];
+      if(!is_bool($configuration["auto_cache"])){
+        throw new InvalidConfigurationException("auto_cache has to be boolean");
+      }
+
+      $this->useCache = $autoCache;
+    }
+
+    if(array_key_exists("cache_lifetime", $configuration)){
+      $defaultCacheLifetime = $configuration["cache_lifetime"];
+      if(!is_int($defaultCacheLifetime) && !is_null($defaultCacheLifetime)){
+        throw new InvalidConfigurationException("cache_lifetime has to be null or int");
+      }
+
+      $this->defaultCacheLifetime = $defaultCacheLifetime;
+    }
+
+    // TODO remove timeout on major update
+    // Set timeout.
+    if (array_key_exists("timeout", $configuration)) {
+      if ((!is_int($configuration['timeout']) || $configuration['timeout'] <= 0) && !($configuration['timeout'] === false)){
+        throw new InvalidConfigurationException("timeout has to be an int > 0 or false");
+      }
+      $this->timeout = $configuration["timeout"];
+    }
+    if($this->timeout !== false){
+      $message = 'The "timeout" configuration is deprecated and will be removed with the next major update.' .
+        ' Set the "timeout" configuration to false and if needed use the set_timeout_limit() function in your own code.';
+      trigger_error($message, E_USER_DEPRECATED);
+      set_time_limit($this->timeout);
+    }
+
+    if(array_key_exists("primary_key", $configuration)){
+      $primaryKey = $configuration["primary_key"];
+      if(!is_string($primaryKey)){
+        throw new InvalidConfigurationException("primary key has to be a string");
+      }
+      $this->primaryKey = $primaryKey;
+    }
+
+    if(array_key_exists("search", $configuration)){
+      $searchConfig = $configuration["search"];
+
+      if(array_key_exists("min_length", $searchConfig)){
+        $searchMinLength = $searchConfig["min_length"];
+        if(!is_int($searchMinLength) || $searchMinLength <= 0){
+          throw new InvalidConfigurationException("min length for searching has to be an int >= 0");
+        }
+        $this->searchOptions["minLength"] = $searchMinLength;
+      }
+
+      if(array_key_exists("mode", $searchConfig)){
+        $searchMode = $searchConfig["mode"];
+        if(!is_string($searchMode) || !in_array(strtolower(trim($searchMode)), ["and", "or"])){
+          throw new InvalidConfigurationException("search mode can just be \"and\" or \"or\"");
+        }
+        $this->searchOptions["mode"] = strtolower(trim($searchMode));
+      }
+
+      if(array_key_exists("score_key", $searchConfig)){
+        $searchScoreKey = $searchConfig["score_key"];
+        if((!is_string($searchScoreKey) && !is_null($searchScoreKey))){
+          throw new InvalidConfigurationException("search score key for search has to be a not empty string or null");
+        }
+        $this->searchOptions["scoreKey"] = $searchScoreKey;
+      }
+
+      if(array_key_exists("algorithm", $searchConfig)){
+        $searchAlgorithm = $searchConfig["algorithm"];
+        if(!in_array($searchAlgorithm, Query::SEARCH_ALGORITHM, true)){
+          $searchAlgorithm = implode(', ', $searchAlgorithm);
+          throw new InvalidConfigurationException("The search algorithm has to be one of the following integer values ($searchAlgorithm)");
+        }
+        $this->searchOptions["algorithm"] = $searchAlgorithm;
+      }
+    }
+  }
+
+  /**
+   * Writes an object in a store.
+   * @param array $storeData
+   * @return array
+   * @throws IOException
+   * @throws IdNotAllowedException
+   * @throws JsonException
+   */
+  private function writeNewDocumentToStore(array $storeData): array
+  {
+    $primaryKey = $this->getPrimaryKey();
+    // Check if it has the primary key
+    if (isset($storeData[$primaryKey])) {
+      throw new IdNotAllowedException(
+        "The \"$primaryKey\" index is reserved by SleekDB, please delete the $primaryKey key and try again"
+      );
+    }
+    $id = $this->increaseCounterAndGetNextId();
+    // Add the system ID with the store data array.
+    $storeData[$primaryKey] = $id;
+    // Prepare storable data
+    $storableJSON = @json_encode($storeData);
+    if ($storableJSON === false) {
+      throw new JsonException('Unable to encode the data array, 
+        please provide a valid PHP associative array');
+    }
+    // Define the store path
+    $filePath = $this->getDataPath()."$id.json";
+
+    IoHelper::writeContentToFile($filePath, $storableJSON);
+
+    return $storeData;
+  }
+
+  /**
+   * Increments the store wide unique store object ID and returns it.
+   * @return int
+   * @throws IOException
+   * @throws JsonException
+   */
+  private function increaseCounterAndGetNextId(): int
+  {
+    $counterPath = $this->getStorePath() . '_cnt.sdb';
+
+    if (!file_exists($counterPath)) {
+      throw new IOException("File $counterPath does not exist.");
+    }
+
+    $dataPath = $this->getDataPath();
+
+    return (int) IoHelper::updateFileContent($counterPath, function ($counter) use ($dataPath){
+      $newCounter = ((int) $counter) + 1;
+
+      while(file_exists($dataPath."$newCounter.json") === true){
+        $newCounter++;
+      }
+      return (string)$newCounter;
+    });
+  }
+
+
+  /**
+   * @param string|int $id
+   * @return int
+   * @throws InvalidArgumentException
+   */
+  private function checkAndStripId($id): int
+  {
+    if(!is_string($id) && !is_int($id)){
+      throw new InvalidArgumentException("The id of the document has to be an integer or string");
+    }
+
+    if(is_string($id)){
+      $id = IoHelper::secureStringForFileAccess($id);
+    }
+
+    if(!is_numeric($id)){
+      throw new InvalidArgumentException("The id of the document has to be numeric");
+    }
+
+    return (int) $id;
+  }
+
+  /**
+   * @return string
+   */
+  private function getDataPath(): string
+  {
+    return $this->getStorePath() . self::dataDirectory;
+  }
+
+}