在MongoEngine中使用reverse_delete_rule時，如何使用循環或前向ReferenceField？

Question

該代碼炸彈：

from mongoengine import * 

class Employee(Document): 
    name = StringField() 
    boss = ReferenceField("Employee", reverse_delete_rule = NULLIFY) 

繼承人的例外：

Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "[…]/mongoengine/base.py", line 791, in __new__ 
    new_class = super_new(cls, name, bases, attrs) 
    File "[…]/mongoengine/base.py", line 630, in __new__ 
    f.document_type.register_delete_rule(new_class, 
    File "[…]/mongoengine/fields.py", line 757, in document_type 
    self.document_type_obj = get_document(self.document_type_obj) 
    File "[…]/mongoengine/base.py", line 136, in get_document 
    """.strip() % name) 
mongoengine.base.NotRegistered: `Employee` has not been registered 
in the document registry. 
Importing the document class automatically registers it, has it 
been imported? 

卸下reverse_delete_rule解決了這個問題，但我想有此規則。

我想這一點，和它的作品，但它確實看起來像廢話，我擔心可能會有不好的副作用（到目前爲止，我還沒有看到任何，雖然）：

from mongoengine import * 

class Employee(Document): 
    pass # required for the reverse_delete_rule to work on the boss field, 
     # because the Employee class needs to exist. 

class Employee(Document): 
    name = StringField() 
    boss = ReferenceField("Employee", reverse_delete_rule = NULLIFY) 

有任何想法嗎？這不應該被視爲MongoEngine中的錯誤嗎？

Answer 1

嘗試使用'self'代替'Employee'：

from mongoengine import * 

class Employee(Document): 
    name = StringField() 
    boss = ReferenceField("self", reverse_delete_rule = NULLIFY) 

查看詳情：https://mongoengine-odm.readthedocs.org/en/latest/guide/defining-documents.html#reference-fields。