Node interface type guessing

types.ex

defmodule MyApp.Web.Schema.Types do
  use Absinthe.Schema.Notation
  use Absinthe.Relay.Schema.Notation
  
  node interface do
    resolve_type fn
      # Guess type from struct name:
      # Example: MyApp.Model.Foo -> :foo
      %{__struct__: str}, _ ->
        str
        |> model_to_node_type
      value, _ ->
        Logger.warn "Could not extract node type from value: #{inspect value}"
        nil
    end
  end
  
  # ...
  
  @doc """
  Given a model name, return the matching node type
  (Absinthe type identifier).

  ## Examples

  ```
  iex> model_to_node_type(MyApp.Model.AssetType)
  :asset_type
  ```
  """
  @spec model_to_node_type(atom) :: atom
  def model_to_node_type(model) do
    ["MyApp", "Model", name] = Module.split(model)
    name
    |> Macro.underscore
    |> String.to_existing_atom
  end  
  
end