Allow tracking whether ActiveType attributes have changed

track_attribute_changes.rb

module TrackAttributeChanges
  extend ActiveSupport::Concern
  include ActiveModel::Dirty

  module ClassMethods
    def track_attribute_changes(attr, type=nil)
      self.module_eval <<-BODY, __FILE__, __LINE__ + 1
        def #{attr}=(value)
          changed = false
          if "#{type}" == "datetime"
            changed = (#{attr}.to_s != value.to_s)
          else
            changed = (#{attr} != value)
          end
          attribute_will_change!('#{attr}') if changed
          super
        end
        def #{attr}_changed?
          changed.include?('#{attr}')
        end
      BODY
    end
  end
end