Class: ActiveRecord::Transaction

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record/transaction.rb

Overview

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.

Constant Summary collapse

NULL_TRANSACTION = 
new(nil).freeze

Instance Method Summary collapse

Constructor Details

#initialize(internal_transaction) ⇒ Transaction

:nodoc:



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# File 'lib/active_record/transaction.rb', line 69

def initialize(internal_transaction) # :nodoc:
  @internal_transaction = internal_transaction
  @uuid = nil
end

Instance Method Details

#after_commit(&block) ⇒ Object

Registers a block to be called after the transaction is fully committed.

If there is no currently open transactions, the block is called immediately, unless the transaction is finalized, in which case attempting to register the callback raises ActiveRecord::ActiveRecordError.

If the transaction has a parent transaction, the callback is transferred to the parent when the current transaction commits, or dropped when the current transaction is rolled back. This operation is repeated until the outermost transaction is reached.

If the callback raises an error, the transaction remains committed.



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# File 'lib/active_record/transaction.rb', line 85

def after_commit(&block)
  if @internal_transaction.nil?
    yield
  else
    @internal_transaction.after_commit(&block)
  end
end

#after_rollback(&block) ⇒ Object

Registers a block to be called after the transaction is rolled back.

If there is no currently open transactions, the block is not called. But if the transaction is finalized, attempting to register the callback raises ActiveRecord::ActiveRecordError.

If the transaction is successfully committed but has a parent transaction, the callback is automatically added to the parent transaction.

If the entire chain of nested transactions are all successfully committed, the block is never called.

If the transaction is already finalized, attempting to register a callback will raise ActiveRecord::ActiveRecordError.



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# File 'lib/active_record/transaction.rb', line 107

def after_rollback(&block)
  @internal_transaction&.after_rollback(&block)
end

#closed? ⇒ Boolean Also known as: blank?

Returns true if the transaction doesn’t exist or is finalized.

Returns:

  • (Boolean) 


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# File 'lib/active_record/transaction.rb', line 117

def closed?
  @internal_transaction.nil? || @internal_transaction.state.finalized?
end

#open? ⇒ Boolean

Returns true if the transaction exists and isn’t finalized yet.

Returns:

  • (Boolean) 


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# File 'lib/active_record/transaction.rb', line 112

def open?
  !closed?
end

#uuid ⇒ Object

Returns a UUID for this transaction or nil if no transaction is open.



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# File 'lib/active_record/transaction.rb', line 124

def uuid
  if @internal_transaction
    @uuid ||= Digest::UUID.uuid_v4
  end
end