Mongoid: cannot embed different classes in one array
===

I have Mongoid classes as follows:

    class Order
      include Mongoid::Document
      embeds_many :games
    end

    class Game
      include Mongoid::Document
      embedded_in :order

      def self.has_gender
        field :gender, type: String
      end
    end

    class Deer < Game
      has_gender
    end

and I get this error when loading Deer:

    undefined method `has_gender' for Deer:Class


Any ideas?