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pagination.ex
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pagination.ex
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defmodule Pleroma.Pagination do
@moduledoc """
Implements Mastodon-compatible pagination.
"""
import Ecto.Query
import Ecto.Changeset
alias Pleroma.Repo
@default_limit 20
def fetch_paginated(query, params) do
options = cast_params(params)
query
|> paginate(options)
|> Repo.all()
|> enforce_order(options)
end
def paginate(query, options) do
query
|> restrict(:min_id, options)
|> restrict(:since_id, options)
|> restrict(:max_id, options)
|> restrict(:order, options)
|> restrict(:limit, options)
end
defp cast_params(params) do
param_types = %{
min_id: :string,
since_id: :string,
max_id: :string,
limit: :integer
}
params =
Enum.reduce(params, %{}, fn
{key, _value}, acc when is_atom(key) -> Map.drop(acc, [key])
{key, value}, acc -> Map.put(acc, key, value)
end)
changeset = cast({%{}, param_types}, params, Map.keys(param_types))
changeset.changes
end
defp restrict(query, :min_id, %{min_id: min_id}) do
where(query, [q], q.id > ^min_id)
end
defp restrict(query, :since_id, %{since_id: since_id}) do
where(query, [q], q.id > ^since_id)
end
defp restrict(query, :max_id, %{max_id: max_id}) do
where(query, [q], q.id < ^max_id)
end
defp restrict(query, :order, %{min_id: _}) do
order_by(query, [u], fragment("? asc nulls last", u.id))
end
defp restrict(query, :order, _options) do
order_by(query, [u], fragment("? desc nulls last", u.id))
end
defp restrict(query, :limit, options) do
limit = Map.get(options, :limit, @default_limit)
query
|> limit(^limit)
end
defp restrict(query, _, _), do: query
defp enforce_order(result, %{min_id: _}) do
result
|> Enum.reverse()
end
defp enforce_order(result, _), do: result
end

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