class Customer < ActiveRecord::Base composed_of :address, :mapping => [ %w(address_street street), %w(address_city city), %w(address_country country) ] composed_of :balance, :class_name => "Money", :mapping => %w(balance amount) end class Address attr_reader :street, :city, :country def initialize(street, city, country) @street, @city, @country = street, city, country end def close_to?(other_address) city == other_address.city && country == other_address.country end end class Money attr_reader :amount, :currency EXCHANGE_RATES = { "USD_TO_DKK" => 6, "DKK_TO_USD" => 0.6 } def initialize(amount, currency = "USD") @amount, @currency = amount, currency end def exchange_to(other_currency) Money.new((amount * EXCHANGE_RATES["#{currency}_TO_#{other_currency}"]).floor, other_currency) end end