Sometimes its handy to do a particular task if an attribute has changed in a model.

You probably only want it to run when an instance is updated, so choose your callback accordingly.

class Post < ActiveRecord::Base
  after_update :notify, :if => :my_attribute_changed?

  def notify
    puts "The Attribute 'my_attribute' has been changed!"
  end
end

Helpful Links:

• Stackoverflow - callback-for-changed-activerecord-attributes