has_many.ex

defmodule ApiEndpoint.Schema.Helpers do
  def has_many({model, foreign_key}, ids) do
    import Ecto.Query

    model
    |> where([m], field(m, ^foreign_key) in ^ids)
    |> Storages.Repo.all
    |> Enum.group_by(fn storage -> Map.get(storage, foreign_key) end)
  end
end

defmodule Users.Types do
  use Absinthe.Schema.Notation

  object :user do
    field :id, :id
    field :first_name, :string
    field :last_name, :string
    field :email, :string
    field :phone, :string
    field :storages, list_of(:storage) do
      resolve fn user, _, _ ->
        batch({ApiEndpoint.Schema.Helpers, :has_many, {Storages.Storage, :user_id}}, user.id, fn batch_result ->
          {:ok, Map.get(batch_result, user.id, [])}
        end)
      end
    end
  end
end