Callbacks

Callbacks are pretty interesting in Mongoid. Just as validations, Mongoid leverages ActiveModel::Callbacks. Callbacks are methods that are called along with persistence. This helps us manipulate the data. We can implement various callbacks such as before_save, after_create, and before_destroy. The entire list of callbacks is available at http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html.

Note

Did you know ActiveModel::Callbacks include after_initialize, after_find, after_touch, after_commit, and after_rollback? Of course, after_commit and after_rollback are specific to transactional databases unlike MongoDB.

Mongoid also supports before_upsert, after_upsert, and around_upsert! As we have seen earlier, an upsert means "update if the document exists and create if it doesn't exist". However, there's more to callbacks in Mongoid.

Mongoid also supports the after_add, after_remove, before_add, and before_remove callback for some specific relations. Let's dive deeper into this...