entrydns/app/models/concerns/stampable.rb

module Stampable
  extend ActiveSupport::Concern

  included do
    belongs_to :creator, :class_name => 'User'
    belongs_to :updator, :class_name => 'User'

    before_create :set_creator_attribute
    before_save   :set_updator_attribute
  end

  def set_creator_attribute
    self.creator = User.current unless creator_id?
  end

  def set_updator_attribute
    self.updator = User.current unless updator_id? && updator_id_changed?
  end
end