Rails - Feb 2006 - newbe: observer setup

Hi All,

Having problem setting up an observer to log changes to
a database.  I have following the Prag Rails book but think
I have something missing.  I am trying a simple puts to see
if the observer is working, but getting nothing on the console.

Here is what I have.  I don''t get any errors.
Thanks for any suggestions/references to debugging.

Dave

The two models:

display_ad.rd

require ''observer''
class DisplayAd < ActiveRecord::Base
   include Observable
   has_many :activities
    #def after_update
     # puts "*************Updated display ad*************"
    #end
end

display_ad_observer.rd

class DisplayAdObserver < ActiveRecord::Observer
   observe DisplayAd

   def after_save(display_ad)
    an_display_ad.logger.info( "Added display ad:
#{an_display_ad.id}")
    puts "*************Saved display ad*************"
   end

   def after_update(display_ad)
    puts "*************Updated display ad*************"
    an_display_ad.logger.info( "Updated display ad: # 
{an_display_ad.id}")
   end
end
DisplayAdObserver.instance

And in environment.rb

  config.active_record.observers = :display_ad_observer