Example of implementing ActiveModel::Dirty on a ActiveFedora::Base subclass

bar_history2.rb

class BarHistory2 < ActiveFedora::Base
  include ActiveModel::Dirty

  has_metadata 'xmlish', :type=>BarStream2
  delegate_to 'xmlish', [:donkey, :cow]

  after_save :clear_changed_attributes

  define_attribute_methods [:donkey, :cow]

  alias_method :_donkey=, :donkey=
  alias_method :_cow=, :cow=

  def donkey= val
    donkey_will_change! unless val == donkey
    self._donkey = val
  end

  def cow= val
    cow_will_change! unless val == cow
    self._cow = val
  end

  def clear_changed_attributes
    @previously_changed = changes
    @changed_attributes.clear
  end
end