Doesn't work for nested transactions

[mrkamel]

after_commit_queue doesn't seem to work for nested transactions, as it stores its queue within the model object and ActiveRecord only runs the after_commit hook once for each uniq record. See https://github.com/rails/rails/blob/master/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb#L80-L89
Thus, if an individual record is updated twice within a single transaction, the run_after_commit runs only once. Compare this overly simplified example:

class MyModel ...
  after_save do
    run_after_commit { puts "run after commit called" }
  end
end

MyModel.transaction do
  model1 = MyModel.find(1)
  model1.title = "1"
  model1.save!

  model2 = MyModel.find(1) # same "record"
  model2.title = "2"
  model2.save!
end

Output is only a single:

run after commit called

If we'd instead save the queue within the transaction object.

module AfterCommitQueue
  # ...

  def after_commit_queue
    self.class.connection.current_transaction.instance_variable_get("@run_after_commit_queue") || self.class.connection.current_transaction.instance_variable_set("@run_after_commit_queue", []) 
  end 

  def clear_after_commit_queue
    self.class.connection.current_transaction.instance_variable_set "@run_after_commit_queue", []
  end
end

It would work as IMO expected. What do you think?