GraphQLHelpers.ex

defmodule GraphqlHelpers do
  import Ecto.Query

  defmacro has_many(model, foreign_key) do
    quote do
      resolve fn subject, _, _ ->
        batch({GraphqlHelpers, :process_has_many, {unquote(model), unquote(foreign_key)}}, subject.id, fn (batch_result) ->
          {:ok, Map.get(batch_result, subject.id, %{})}
        end)
      end
    end
  end

  defmacro belongs_to(model) do
    quote do
      resolve fn subject, _, _ ->
        [_ | module] = Module.split(unquote(model))
        key = Macro.underscore(module |> List.last) <> "_id" |> String.to_atom
        id = Map.get(subject, key)

        batch({GraphqlHelpers, :process_belongs_to, unquote(model)}, id, fn batch_result ->
          {:ok, Map.get(batch_result, id, %{})}
        end)
      end
    end
  end

  def process_has_many({model, foreign_key}, ids) do
    model
    |> where([m], field(m, ^foreign_key) in ^ids)
    |> ApiEndpoint.Repo.all
    |> Enum.group_by(fn record -> Map.get(record, foreign_key) end)
  end

  def process_belongs_to(model, ids) do
    model
    |> where([m], m.id in ^ids)
    |> ApiEndpoint.Repo.all
    |> Map.new(&{&1.id, &1})
  end
end


defmodule Storages.Types do
  use Absinthe.Schema.Notation
  import GraphqlHelpers

  object :storage do
    field :id, :id
    field :title, :string
    field :description, :string
    field :slug, :string
    field :status, :string
    field :latitude, :float
    field :longitude, :float
    field :user, :user, do: belongs_to(Users.User)
  end
end

defmodule Users.Types do
  use Absinthe.Schema.Notation
  import GraphqlHelpers

  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: has_many(Storages.Storage, :user_id)
  end
end