Question

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.

Answer 1

I think transaction_include_action? is what you are after. It gives a reliable indication of the specific transaction in process (verified in 3.0.8).

Formally, it determines if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.

class Item < ActiveRecord::Base
  after_commit lambda {    
    Rails.logger.info "transaction_include_action?(:create): #{transaction_include_action?(:create)}"
    Rails.logger.info "transaction_include_action?(:destroy): #{transaction_include_action?(:destroy)}"
    Rails.logger.info "transaction_include_action?(:update): #{transaction_include_action?(:update)}"
  }
end

Also of interest may be transaction_record_state which can be used to determine if a record was created or destroyed in a transaction. State should be one of :new_record or :destroyed.

Update for Rails 4

For those seeking to solve the problem in Rails 4, this method is now deprecated, you should use transaction_include_any_action? which accepts an array of actions.

Usage Example:

transaction_include_any_action?([:create])