apple.rb

class Apple
  include Fruit

  property :colour, Enum[:red, :green]
end

fruit.rb

module Fruit
  def self.included(base)
    include DataMapper::Resource

    property :id,         Serial
    property :juiciness,  Integer
    property :price,      Integer
    property :name,       String
  end
end

orange.rb

class Orange
  include Fruit

  property :type, Enum[:navel, :valencia, :blood]
end