A pseudo-OODB style of using MongoMapper's plugin system to create composed objects.

composition_over_inheritance_in_mongo_mapper.rb

#rvm use 1.9.2
#brew install mongo
#gem install mongo_mapper
#gem install bson_ext

require 'rubygems'
require 'mongo_mapper'

MongoMapper.database = 'mm_demo'

module MMDemo
  module HasDoorsAndWindows
    def self.configure(model)
      model.key :doors, Integer, :default => 0
      model.key :windows, Integer, :default => 0
      model.key :sun_roof, Boolean, :default => false
    end
    
    module InstanceMethods
      def enterable?
        doors > 0
      end
      
      def well_lit?
        windows >= (doors * 5)
      end
    end
  end
end


class House
  include MongoMapper::Document
  
  plugin MMDemo::HasDoorsAndWindows
end

class Vehicle
  include MongoMapper::Document
  
  key :wheels, Integer
end

class Motorcyle < Vehicle
end

class Car < Vehicle
  plugin MMDemo::HasDoorsAndWindows
  def well_lit?
    sunroof?
  end
end

require 'minitest/autorun'

describe "a House" do
  it "has doors" do
    House.new(:doors => 2).doors.must_equal 2
  end
  
  it "has windows" do
    House.new(:doors => 7).doors.must_equal 7
  end
  
  it "is enterable if there are any doors" do
    House.new(:doors => 0).enterable?.must_equal false
    House.new(:doors => 4).enterable?.must_equal true
  end
  
  it "is enterable if there are any doors" do
    House.new(:doors => 0).enterable?.must_equal false
    House.new(:doors => 4).enterable?.must_equal true
  end
  
  it "is well lit if there are 5x as many windows as doors" do
    House.new(:doors => 1, :windows => 5).well_lit?.must_equal true
    House.new(:doors => 1, :windows => 4).well_lit?.must_equal false
  end
end

describe "a Car" do
  it "is well lit if it has a sunroof" do
    Car.new(:sunroof => true).well_lit?.must_equal true
    Car.new(:sunroof => false).well_lit?.must_equal false
  end
end