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

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

Answer 1

I'm curious to know why you couldn't move your after_commit logic into after_create and after_update. Is there some important state change that happens between the latter 2 calls and after_commit?

If your create and update handling has some overlapping logic, you could just have the latter 2 methods call a third method, passing in the action:

# Tip: on ruby 1.9 you can use __callee__ to get the current method name, so you don't have to hardcode :create and :update.
class WidgetObserver < ActiveRecord::Observer
  def after_create(rec)
    # create-specific logic here...
    handler(rec, :create)
    # create-specific logic here...
  end
  def after_update(rec)
    # update-specific logic here...
    handler(rec, :update)
    # update-specific logic here...
  end

  private
  def handler(rec, action)
    # overlapping logic
  end
end

If you still rather use after_commit, you can use thread variables. This won't leak memory as long as dead threads are allowed to be garbage-collected.

class WidgetObserver < ActiveRecord::Observer
  def after_create(rec)
    warn "observer: after_create"
    Thread.current[:widget_observer_action] = :create
  end

  def after_update(rec)
    warn "observer: after_update"
    Thread.current[:widget_observer_action] = :update
  end

  # this is needed because after_commit also runs for destroy's.
  def after_destroy(rec)
    warn "observer: after_destroy"
    Thread.current[:widget_observer_action] = :destroy
  end

  def after_commit(rec)
    action = Thread.current[:widget_observer_action]
    warn "observer: after_commit: #{action}"
  ensure
    Thread.current[:widget_observer_action] = nil
  end

  # isn't strictly necessary, but it's good practice to keep the variable in a proper state.
  def after_rollback(rec)
    Thread.current[:widget_observer_action] = nil
  end
end