Mongoid dependent :destroy vs :delete

Question

When using Mongoid referenced reletions what's the diffrence between dependent detroy and dependent delete since in the docs it tells:

:delete: Delete the child documents.
:destroy: Destroy the child documents.

Answer 1

In Mongoid (and also ActiveRecord I believe), delete just removes the object from the database. destroy will delete the object and run all of the appropriate callbacks that the model has defined. So if you have a before_destroy callback on a model and you delete an instance of that model, the before_destroy callback will not be called.

So dependent: :destroy runs the model's callbacks when deleting and dependent: :delete does not.

Answer 2

• destroy runs model callbacks and then makes a REMOVE query to the DB.
• delete just makes a REMOVE query to the DB.

The names are taken from ActiveRecord, that's why they don't match mongo very well.

You could see delete as an optimization over destroy. When you use destroy, you make sure that before_destroy callbacks are executed, so proper cleanup is done. In the other hand, if you do something like Model.destroy_all, it has to load ALL elements, and then make a REMOVE query for each of them, whether Model.delete_all makes just one query.