Rails - Jan 2006 - association callbacks

Hello all. I am looking for some feedback on an implementation.  I''m
writing
a plugin that will log all model changes.  I do not want to have to add a
line a code for this functionality every time I create a model.  Instead I
create a table with the name <model>_changes.

The basic stuff was easy:

      base.after_create {|model|
        model.log_create if model.has_backup_table?
      }
**also log on before_update and before_destroy

What I''m curious about is the habtm relationships.  I wanted to keep
track
of when this changes as well. An example would be changing a user''s
role.

So I did this:
  def self.included(base)
    ...
      base.before_validation{|model|
        model.class.append_habtm_callbacks if model.has_backup_table?
      }
  ...
  end

  module ClassMethods
      def append_habtm_callbacks
        reflect_on_all_associations.each{ |association|
          if association.macro == :has_and_belongs_to_many
            #add_callback
            add_callback = "before_add_for_#{association.name}"
            class_inheritable_reader(add_callback.to_sym)
            write_inheritable_array(add_callback.to_sym, [:log_add])
            #remove_callback
            remove_callback = "before_remove_for_#{association.name}"
            class_inheritable_reader(remove_callback.to_sym)
            write_inheritable_array(remove_callback.to_sym, [:log_remove])
          end
        }
      end
   end#end ClassMethods


This works well and the only way I found to do this without:
1) Didn''t want to have to require code in the model. I wanted it to be
"smart".
2) Didn''t want to "alias_method" any Rails code.  I thought
using what''s
available was a better approach in this case.

Thoughts?

Thanks for any feedback,
andy

p.s. Sorry for the lengthy email...tried to keep it as short as possible.
--
Andrew Stone
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://wrath.rubyonrails.org/pipermail/rails/attachments/20060113/032f30b3/attachment.html

Hey Andrew!

Rails already has support for association callbacks:

You can read about it in the "association callbacks" section here:

http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html

Ciao!
Florian