How to access parent module in Elixir?

Question

I have a general-purpose loader for fetching records from a database:

defmodule Loader do
  defmacro __using__(opts) do
    quote location: :keep, bind_quoted: [schema: opts[:schema]] do

      def one(id), do: unquote(schema) |> Repo.get(id)
      def all,     do: unquote(schema) |> Repo.all
    end
  end
end

and particular loaders fro specific schemas:

defmodule Location.Loader do
  use Loader, schema: Location
end

Is there any way to communicate with "used" module in some other way e.g. __MODULE__.parent?

What is it that you would like to do? You can refer to the module by name like any other module. — Gazler
– Gazler, Commented Apr 26, 2016 at 8:13
The thing you are trying to do looks a little bit overcomplicated. I would also like to know what are you trying to achieve. — tkowal
– tkowal, Commented Apr 26, 2016 at 8:46
As you can see, I want to have access in Loader to Location which is a "top" module of a module where Loader is used. — Kamil Lelonek
– Kamil Lelonek, Commented Apr 26, 2016 at 8:46
What is the reason you want to access Loader. What do you mean by "access" - call functions? If so you can call public functions with Loader.some_function(). There is no way to call private functions from another module. — Gazler
– Gazler, Commented Apr 26, 2016 at 8:56
I want to use Location.Loader.all or Location.Loader.one(123). The thing is that I want to know somehow in general Loader, the name of module it is invoked from e.g. Location.Loader. I achieved that by passing this in opts but i wonder if there's any other way to do so. — Kamil Lelonek
– Kamil Lelonek, Commented Apr 26, 2016 at 10:26

Dogbert · Accepted Answer · 2016-04-26 10:57:43Z

2

You can use __MODULE__ from inside the quote of Loader.__using__, and use Module.split/1, Enum.drop/2, and Module.concat/1 to get the parent module.

defmodule Loader do
  defmacro __using__(opts) do
    quote location: :keep, bind_quoted: [schema: opts[:schema]] do
      @parent_module __MODULE__ |> Module.split |> Enum.drop(-1) |> Module.concat
      def one(id), do: IO.puts("#{@parent_module}:one:#{id}")
      def all,     do: IO.puts("#{@parent_module}:all")
    end
  end
end

defmodule Location.Loader do
  use Loader
end

Location.Loader.one 123
Location.Loader.all

prints

Elixir.Location:one:123
Elixir.Location:all

But, I would recommend not using this and using your original code as it's more explicit, and from my experience, considered more idiomatic.

answered Apr 26, 2016 at 10:57

Dogbert

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