debianize-mobilizon/lib/mobilizon/storage/page.ex

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2019-09-08 01:49:56 +02:00
defmodule Mobilizon.Storage.Page do
@moduledoc """
Module for pagination of queries.
"""
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import Ecto.Query
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alias Mobilizon.Storage.Repo
defstruct [
:total,
:elements
]
@type t(structure) :: %__MODULE__{
total: integer,
elements: list(structure)
}
@doc """
Returns a Page struct for a query.
`field` is use to define the field that will be used for the count aggregate, which should be the same as the field used for order_by
See https://stackoverflow.com/q/12693089/10204399
"""
@spec build_page(Ecto.Queryable.t(), integer | nil, integer | nil, atom()) :: t(any)
def build_page(query, page, limit, field \\ :id) do
[total, elements] =
[
fn -> Repo.aggregate(query, :count, field) end,
fn -> Repo.all(paginate(query, page, limit)) end
]
|> Enum.map(&Task.async/1)
|> Enum.map(&Task.await(&1, 15_000))
%__MODULE__{total: total, elements: elements}
end
@doc """
Add limit and offset to the query.
"""
@spec paginate(Ecto.Queryable.t() | struct, integer | nil, integer | nil) :: Ecto.Query.t()
def paginate(query, page \\ 1, size \\ 10)
def paginate(query, page, _size) when is_nil(page), do: paginate(query)
def paginate(query, page, size) when is_nil(size), do: paginate(query, page)
def paginate(query, page, size) do
from(query, limit: ^size, offset: ^((page - 1) * size))
end
end