Mongoengine: two-way reference raise NotRegistered Exception when using reverse_delete_rule

[chenli0906]

code as below:

class A(Document):
    name = StringField()
    ref_b= ListField(ReferenceField('B', reverse_delete_rule=PULL))

class B(Document):
    content = StringField()
    ref_a = ReferenceField('A', reverse_delete_rule=NULLIFY)

User Doc has a forward references Page， when i set a reverse_delete_rule other than DO_NOTHING，it will raise
mongoengine.errors.NotRegistered: `B` has not been registered in the document registry. Importing the document class automatically registers it, has it been imported?

I want to automatically delete reference when I delete document

how can i avoid this Exception？

[reasonman]

I worked around this by separating the delete rule for model that referenced the "unregistered" model. I had to register the delete rule for the model defined first(User in your example). Yours would look like this I think:

class User(Document):
    name = StringField()
    ref_page= ListField(ReferenceField('Page'))

class Page(Document):
    content = StringField()
    ref_user = ReferenceField(User, reverse_delete_rule=NULLIFY)

User.register_delete_rule(Page, "ref_page", PULL)

[chenli0906]

@reasonman Yes，that’s it， I find it in API Reference, Thanks a lot!