Transactions
On this page
Version 4.0 of the MongoDB server introduces multi-document transactions. (Updates to multiple fields within a single document are atomic in all versions of MongoDB). Transactions require Mongoid version 6.4 or higher and Ruby driver version 2.6 or higher.
Using Transactions
In order to start a transaction, the application must have a session.
A transaction can be started by calling the start_transaction
method on a session, which can be
obtained by calling the with_session
method on either a model class or instance:
class Person include Mongoid::Document end Person.with_session do |session| session.start_transaction end person = Person.new person.with_session do |session| session.start_transaction end
It is also possible to specify read concern, write concern and read preference when starting a transaction:
Person.with_session do |session| session.start_transaction( read_concern: {level: :majority}, write_concern: {w: 3}, read: {mode: :primary}) end
A transaction may be committed or aborted. The corresponding methods to do so are
commit_transaction
and abort_transaction
, again on the session instance:
Person.with_session do |session| session.commit_transaction end Person.with_session do |session| session.abort_transaction end
If a session ends with an open transaction, the transaction is aborted.
The transaction commit can be retried if it fails. Here is the Ruby code to do so:
begin session.commit_transaction rescue Mongo::Error => e if e.label?(Mongo::Error::UNKNOWN_TRANSACTION_COMMIT_RESULT_LABEL) retry else raise end end
Note that in order to perform operations within the transaction, operations must use the same client that the session was initiated on. By default, all operations will be done on the default client:
class Person include Mongoid::Document end class Post include Mongoid::Document end Person.with_session do |s| s.start_transaction Person.create! Person.create! Post.create! s.commit_transaction end
To explicitly use a different client, use the with
method:
Post.with(client: :other) do Person.with(client: :other) do Person.with_session do |s| s.start_transaction Person.create! Person.create! Post.create! s.commit_transaction end end end