How can I tell when an ActiveRecord::Base.transaction block commits?

Question

A common problem with background jobs and ActiveRecord is when jobs get enqueued and executed before a needed model is committed to the database.

ActiveRecord models have a nice after_commit callback that can be used for a particular model.

But let's say you've got some business logic that touches a few different models, and it's not really appropriate to cram that logic inside a single model. So, you write some sort of service/command object that performs the logic inside a transaction block:

For example, something along the lines of:

class SomeServiceObject

  def execute
    thing = create_thing_in_a_tx

    # this notification often fires before the above transaction commits.
    notify_user(thing)
  end

  private

  def create_thing_in_a_tx
    ActiveRecord::Base.transaction do
      a = ModelA.new(foo: 'bar')
      b = ModelB.new(a_record: a, biz: 'baz')
      #... various other logic that doesn't really belong in a model ...
      ThingModel.create!(b_record: b)
    end
  end

  def notify_user(thing)
    EnqueueJob.process_asyc(thing.id)
  end
end

In this case, as far as I can tell, you don't really have access to the handy after_commit callback.

I suppose in the above example, you could have ThingModel enqueue the job inside of its after_commit callback, but then you're spreading what should be the responsibilities of SomeServiceObject across different classes, and that feels wrong.

Given all of the above, is there any reasonable way to know when a ActiveRecord::Base.transaction block commits, without resorting to any particular model's after_commit callback?

Thank you! :-D

(See also: How to force Rails ActiveRecord to commit a transaction flush)

Answer 1

It's simpler than you might think. After the ActiveRecord::Base.transaction block completes, the transaction has been committed.

def create_thing_in_a_tx
  begin
    ActiveRecord::Base.transaction do
      a = ModelA.new(foo: 'bar')
      b = ModelB.new(a_record: a, biz: 'baz')
      #... various other logic that doesn't really belong in a model ...
      ThingModel.create!(b_record: b)
    end
    # The transaction COMMIT has happened.  Do your after commit logic here.
  rescue # any exception
    # The transaction was aborted with a ROLLBACK.  
    # Your after commit logic above won't be executed.
  end
end