In what direction does mongoengine reverse_delete_rule work?

Question

If I have the following two models:

class User(Document):
    ...

class Profile(Document):
    user = ReferenceField(reverse_delete_rule=CASCADE)

Does deleting a User instance delete its Profile? Does deleting its Profile delete the user?

There seams to be an error in the documentation:

class Employee(Document):
    ...
    profile_page = ReferenceField('ProfilePage', reverse_delete_rule=mongoengine.NULLIFY)

The declaration in this example means that when an Employee object is removed, the ProfilePage that belongs to that employee is removed as well. If a whole batch of employees is removed, all profile pages that are linked are removed as well.

The code uses NULLIFY, but the explanation indicates the use of CASCADE. or am I misunderstanding something?

Answer 1

Deleting a User instance deletes its Profile. This is the way reverse_delete_rule=CASCADE works. Just like in Relational Databases.

You may check this code:

from mongoengine import connect, Document, ReferenceField, CASCADE


connect('test_cascade')


class User(Document):
    pass


class Profile(Document):
    user = ReferenceField(User, reverse_delete_rule=CASCADE)


user = User().save()
profile = Profile(user=user).save()

user.delete()

assert Profile.objects.count() == 0

They also updated documentation, now it's other way around:

class ProfilePage(Document):
    ...
    employee = ReferenceField('Employee', reverse_delete_rule=mongoengine.CASCADE)

The declaration in this example means that when an Employee object is removed, the ProfilePage that references that employee is removed as well. If a whole batch of employees is removed, all profile pages that are linked are removed as well.