In ActiveRecord save and destroy operations are automatically wrapped in a transaction. Therefore, all transactional callbacks work even if a user did not explicitly open a transaction.

This is an expected behavior for this feature. It is basically impossible to implement it in Mongoid without an implicit transaction. We can just get somehow close to it.

• We should allow users to enable implicit transactions in Mongoid.
• It should be documented that this option will not work on a standalone deployment
• We should provide tools to run a replica set deployment locally, or document how to do it.