Ecto Model Schema Extension

product.ex

defmodule Nectar.ExtendProduct do
  Module.register_attribute(__MODULE__, :schema_changes, accumulate: true)
  add_to_schema = fn(schema_change) -> Module.put_attribute(__MODULE__, :schema_changes, schema_change) end
    
  add_to_schema.(quote do: (field :special, :boolean, virtual: true))
    
  defmacro extensions do
    @schema_changes
  end
end

defmodule Nectar.Product do
  import Nectar.ExtendProduct
  
  schema do
    extensions
  end
  
  ## Add #special boolean to get casted
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, ~w(special))
  end
end