Rails activerecord after_create vs after_create_commit

Background

I was working on a chat application. Pusher was used as a real-time communication layer between the server and the client. Here the pusher event was triggered after creating a message. Which is simple and it works perfectly.

after_create :notify_pusher
private
def notify_pusher
  pusher.trigger('my-channel', 'my-event', {
    message: 'hello world'
  })
end

This works only for text messages. I have noticed an issue when sending a photo message. While sending a photo message, sent message is appearing to the receiver chat box with empty attachment. After debugging I found something is wrong with the after_create ActiveRecord callback used. Since I was using ActiveStorage, I started to search if there is any callback in ActiveStorage which triggers after upload attachment. Unfortunately, there is no such callback concept in ActiveStorage. While looking the RailsGuide I found something interesting

It’s important to know that the file is not yet available in the after_create callback but in the after_create_commit only.

This looks interesting.

Rails Guide Says:

after_create(*args, &block) => Registers a callback to be called after a record is created.

after_create_commit(*args, &block) => This callback is called after a record has been created

Both look similar, right?

So, what made the difference in my codebase?

Your code doesn’t execute until after the outermost transaction has been committed when using after_create_commit. If you wanted to make many changes in a single transaction, you could use the existing transaction rails or one you developed.

Your create/save may still be rolled back at the time after_save/create executes, and (by default) it won’t be accessible to other database connections, file upload (such as a background process like sidekiq). Using after_create_commit is typically driven by one of these two factors in some combination.

References

https://pusher.com/
https://guides.rubyonrails.org/active_storage_overview.html#downloading-files
https://stackoverflow.com/questions/33890458/difference-between-after-create-after-save-and-after-commit-in-rails-callbacks