games.ex

defmodule Vassal.Game do
  # ... bunch of stuff ..
  
  @doc false
  def changeset(%Game{} = game, attrs) do
    game
    |> cast(attrs, [:name, :year, :players, :length, :series, :description])
    |> cast_assoc(:publisher)
    |> cast_assoc(:era)
    |> cast_assoc(:topic)
    |> cast_scale(:scale)
    |> validate_required([:name, :year, :players, :length, :series, :description])
    |> unique_constraint(:name)
  end

  def cast_scale(changeset) do
    scale = case Map.get(changeset.params, "scale", %{}) do
      %{ "id" => id } ->
        Vassal.Games.get_scale(id)
      %{ "name" => name } ->
        %Scale{ name: name }
      _ ->
        %Scale{}
    end

    put_assoc(changeset, :scale, scale)
  end
end