Rails geocoder attribute

In the rails is it possible to make a function that everytime a particular attribute is changed, rails executes a function. In my case, everytime object.address (I have geocoded_by :address and after_validation :geocode) is changed, I want to do object.geocode. I am on rails 3

The best solution, I think would be to include ActiveModel::Dirty in your model, then you can check it in a callback

class MyModel < ActiveRecord::Base
  def after_save
     if address_changed? do
       #some stuff..
     end
  end
end

see ActiveModel::Dirty