Rails - Nov 2014 - Metaprogramming Q: Calling an external class method on after_save

I have the following classes:

    class AwardBase
    class AwardOne < AwardBase
    class Post < ActiveRecord::Base

The Post is an ActiveRecord, and the Award has a can_award? class method 
which takes a post object and checks to see if it meets some criteria. If 
yes, it updates post.owner.awards.

I know I can do this using an Observer pattern (I tested it and the code 
works fine). However, that requires me to add additional code to the model. 
I'd like not to touch the model at all if possible. What I'd like to do
is
run the Award checks like this (the trigger will be invoked at class load 
time):

    class AwardOne < AwardBase
      trigger :post, :after_save

      def self.can_award?(post)
        ...
      end
    end

The intention with the above code is that it should automatically add 
AwardOne.can_award? to Post's after_save method

So essentially what I'm trying to do is to get the above code to be 
equivalent to:

    class Post < ActiveRecord::Base
      after_save AwardOne.can_award?(self)
      ...
    end

which is basically:

    class Post < ActiveRecord::Base
      after_save :check_award

      def check_award
        AwardOne.can_award?(self)
      end
    end

How can I do this without modifying the Post class?

----------------------------------

Here's what I've done (which does not appear to work):

    class AwardBase

      def self.trigger (klass, active_record_event)
        model_class = klass.to_class

        this = self
        model_class.instance_eval do
          def award_callback
            this.can_award?(self)
          end
        end

        model_class.class_eval do
          self.send(active_record_event, :award_callback)
        end
      end

      def self.can_award? (model)
        raise NotImplementedError
      end
    end

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To view this discussion on the web visit
https://groups.google.com/d/msgid/rubyonrails-talk/976a57ed-c4e2-484c-9042-c279c5db70c2%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.