ComposableOfMoney: currency attributes in ActiveRecord

composable_of_money.rb

##
# Aggregation
# http://ar.rubyonrails.org/classes/ActiveRecord/Aggregations/ClassMethods.html

module ComposableOfMoney

  extend ActiveSupport::Concern

  included do

    def self.composed_of_money(attr)
      composed_of attr,
        :class_name => "Money",
        :mapping => [["#{attr}_cents", "cents"]],
        :constructor => Proc.new { |cents|
          Money.new(cents || 0, Money.default_currency) },
        :converter => Proc.new { |value|
          raise "Can't convert #{value.class} to Money" unless value.respond_to?(:to_money)
          value.to_money }
    end

  end

end

example.rb

class Example < ActiveRecord::Base
  include ComposableOfMoney
  composed_of_money :price
end