Rails Cache Sweeper and Model Callback Firing

Question

I have the following classes:

class Vigil < ActiveRecord::Base
  after_update :do_something_cool

  private
    def do_something_cool
      # Sweet code here
    end
end

class NewsFeedObserver < ActionController::Caching::Sweeper
  observe Vigil

  def after_update
    # Create a news feed entry
  end
end

Everything works as expected; however, the after_update in the sweeper requires that the do_something_cool method in the model has finished before it can run properly. The problem is that the after_update in the sweeper is being called before (or perhaps at the same time as) the do_something_cool callback and it's causing problems.

Does anyone know how to force the after_update in the sweeper to fire after the model callback? Is there better way to achieve this?

Update/Fix: As it turns out, unlike the answer below states, the observer callbacks actually ARE firing in the correct order (after the model callbacks). When I discovered this, I realized something else must be wrong.

The do_something_cool method destroys all of a vigil's slots, and replaces them with the correct number of slots with the correct times. The observer relies on the number of slots to figure out how long the vigil should last. So, the underlying problem was that all of the vigil's slots were being destroyed, and that data was cached, so when I called vigil.slots from the observer, it was using the cached (destroyed slots) data. The solution: simply call vigil.slots(true) at the end of do_something_cool to reload/recache the newly created slots!

deanWombourne deanWombourne · Accepted Answer · 2010-03-11T17:30:14

It's not going to be running at the same time but you're right, it looks like the Sweeper callback is being run before the Model one.

This post might be helpful : http://upstre.am/2007/10/27/using-and-testing-activerecordrails-observers/

About halfway down (search for 'callback :after_read') they have tried to create custom callbacks for their observers. You could use this to create a after_something_cool ARObserver method that gets called when the Model is done being cool e.g.

class Vigil < ActiveRecord::Base
  after_update :do_something_cool

  private
    def do_something_cool
      # Sweet code here
      callback :after_something_cool
    end
end

class NewsFeedObserver < ActionController::Caching::Sweeper
  observe Vigil

  def after_something_cool
    # Create a news feed entry
  end
end

Disclaimer: I've never done this and I've always found sweepers to be temperamental between rails versions so what worked for them might not work for you :(

Rails Cache Sweeper and Model Callback Firing

1 Answers