ActiveRecord::Transaction

Class specifies the interface to interact with the current transaction state.

It can either map to an actual transaction/savepoint, or represent the absence of a transaction.

State

We say that a transaction is finalized when it wraps a real transaction that has been either committed or rolled back.

A transaction is open if it wraps a real transaction that is not finalized.

On the other hand, a transaction is closed when it is not open. That is, when it represents absence of transaction, or it wraps a real but finalized one.

You can check whether a transaction is open or closed with the open? and closed? predicates:

if Article.current_transaction.open?
  # We are inside a real and not finalized transaction.
end

Closed transactions are `blank?` too.

Callbacks

After updating the database state, you may sometimes need to perform some extra work, or reflect these changes in a remote system like clearing or updating a cache:

def publish_article(article)
  article.update!(published: true)
  NotificationService.article_published(article)
end

The above code works but has one important flaw, which is that it no longer works properly if called inside a transaction, as it will interact with the remote system before the changes are persisted:

Article.transaction do
  article = create_article(article)
  publish_article(article)
end

The callbacks offered by ActiveRecord::Transaction allow to rewriting this method in a way that is compatible with transactions:

def publish_article(article)
  article.update!(published: true)
  Article.current_transaction.after_commit do
    NotificationService.article_published(article)
  end
end

In the above example, if publish_article is called inside a transaction, the callback will be invoked after the transaction is successfully committed, and if called outside a transaction, the callback will be invoked immediately.

Caveats

When using after_commit callbacks, it is important to note that if the callback raises an error, the transaction won’t be rolled back as it was already committed. Relying solely on these to synchronize state between multiple systems may lead to consistency issues.