Alex Rivera | Logout

Rails 3: How to identify after_commit action in observers? (create/update/destroy)

Asked 2011-08-30T04:26:20.793
68

I have an observer and I register an after_commit callback. How can I tell whether it was fired after create or update? I can tell an item was destroyed by asking item.destroyed? but #new_record? doesn't work since the item was saved.

I was going to solve it by adding after_create/after_update and do something like @action = :create inside and check the @action at after_commit, but it seems that the observer instance is a singleton and I might just override a value before it gets to the after_commit. So I solved it in an uglier way, storing the action in a map based on the item.id on after_create/update and checking its value on after_commit. Really ugly.

Is there any other way?

Update

As @tardate said, transaction_include_action? is a good indication, though it's a private method, and in an observer it should be accessed with #send.

class ProductScoreObserver < ActiveRecord::Observer
  observe :product

  def after_commit(product)
    if product.send(:transaction_include_action?, :destroy)
      ...

Unfortunately, the :on option does not work in observers.

Just make sure you test the hell of your observers (look for test_after_commit gem if you use use_transactional_fixtures) so when you upgrade to new Rails version you'll know if it still works.

(Tested on 3.2.9)

Update 2

Instead of Observers I now use ActiveSupport::Concern and after_commit :blah, on: :create works there.

ruby-on-rails ruby-on-rails-3 transactions observer-pattern
Edit
Report

2 Answers

7

You can solve by using two techniques.

  • The approach suggested by @nathanvda i.e. checking the created_at and updated_at. If they are same, the record is newly created, else its an update.

  • By using virtual attributes in the model. Steps are:

    • Add a field in the model with the code attr_accessor newly_created

    • Update the same in the before_create and before_update callbacks as 

      def before_create (record)
    record.newly_created = true
end

def before_update (record)
    record.newly_created = false
end
answered 2011-10-07T14:03:55.803
4

Based on leenasn idea, I created some modules that makes it possible to use after_commit_on_updateand after_commit_on_create callbacks: https://gist.github.com/2392664

Usage:

class User < ActiveRecord::Base
  include AfterCommitCallbacks
  after_commit_on_create :foo

  def foo
    puts "foo"
  end
end

class UserObserver < ActiveRecord::Observer
  def after_commit_on_create(user)
    puts "foo"
  end
end
answered 2012-04-15T13:02:19.837

Your Answer