It's impossible to add a custom callback to AR class

[romanbsd]

Consider the following:

class Post
  define_model_callbacks :approve, :only => :after

    def approve!
      run_callbacks(:approve) do
        update_attribute(:approved, true)
      end
    end
end

class PostObserver
  def after_approve(post)
    # do something
  end
end

This won't work as expected, because ActiveRecord::Observer defines the notify methods using the following code:

      def define_callbacks(klass)
        observer = self
        observer_name = observer.class.name.underscore.gsub('/', '__')

        ActiveRecord::Callbacks::CALLBACKS.each do |callback|
          next unless respond_to?(callback)
          callback_meth = :"_notify_#{observer_name}_for_#{callback}"
          unless klass.respond_to?(callback_meth)
            klass.send(:define_method, callback_meth) do |&block|
              observer.update(callback, self, &block)
            end
            klass.send(callback, callback_meth)
          end
        end
      end

Therefore only ActiveRecord::Callbacks::CALLBACKS are going to be used.

[lacco]

It's a pity that this doesn't work out of the box. Workaround for the moment:

class Post
  define_model_callbacks :approve, :only => :after

  def approve!
    run_callbacks(:approve) do
      update_attribute(:approved, true)
      notify_observers :after_approve
    end
  end
end

[lacco]

I moved the notifying call into an own method, so that you just have to use define_model_callbacks_for_observersinstead of ``define_model_callbacks` (you might want to put this into a module):

  def define_model_callbacks_for_observers(*args)
    types = Array.wrap(args.extract_options![:only] || [:before, :around, :after])

    callbacks = define_model_callbacks(*args)

    callbacks.each do |callback|
      types.each do |filter|
        set_callback(callback, filter) do
          notify_observers :"#{filter}_#{callback}"
          true
        end
      end
    end
  end

[ahawkins]

@romanbsd It is possible. You have to use notify_observers. Here is the snippet I use in my code:

def notify_of_finished
   changed ; Todo.notify_observers :finished, self ; true
end

This works perfectly. I think this the correct approach. I don't like extending the Rails callbacks using the proposed approach.

@lacco interested in submitting a Pull Request?

[carlosantoniodasilva]

Hey, I'm closing this as stale, if anyone wants to try out a pull request, please go ahead. You can gather more feedback first if you want in the Rails Core mailing list. Thanks.