Add transaction method to Mongoid module. This method accepts a block, and all operation inside the block are wrapped in a mongodb transaction.

Successful Transaction

Mongoid.transaction do
  # ...
end

will result in:

• Default client starts a new session.
• A transaction is started on the created session.
• All the server commands issued by the code inside the block are sent with the session option.
• When the block is completed, the transaction is committed.

Failed Transaction
Failed transaction means that the code inside the transaction block raises an exception.

Mongoid.transaction do
  # ...
  raise SomeError
  # ...
end

will result in:

• Default client starts a new session (see more about used clients below).

NOTE
Callbacks are not in the scope of this ticket.

• A transaction is started on the created session.
• All the server commands issued by the code inside the block before the exception are sent with the session option.
• When the exception is raised, the transaction is aborted.