before_changes

before_changes.rb

module BeforeChanges
  def before_changes
    before_change_object = self.clone
    changes.each do |changed_field, change|
       before_change_object.send("#{changed_field}=", change[0])
    end
    before_change_object
  end
end

module ActiveRecord
  class Base
    include BeforeChanges
  end
end

class Post < ActiveRecord::Base
end


>> post = Post.first
#<Post:0x3434> {
 :title => 'Joker'
}
>> post.title = 'Joker owned Batman'
'Joker owned Batman'

>> post.before_changes
#<Post:0x5678> {
  :title => 'Joker'
}