forward-declaration - 在 MongoEngine 中使用 reverse_delete_rule 时如何拥有循环或前向 ReferenceField？

Question

此代码炸弹：

from mongoengine import *

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

继承人例外：

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?

删除reverse_delete_rule修复问题，但我想有这个规则。

我试过这个，它有效，但它看起来真的很垃圾，我担心可能会有不好的副作用（到目前为止，我还没有看到任何副作用）：

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)

有任何想法吗？这不应该被视为 MongoEngine 中的错误吗？

Answer 1

尝试'self'改用'Employee'：

from mongoengine import *

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

查看详细信息：https ://mongoengine-odm.readthedocs.org/en/latest/guide/defining-documents.html#reference-fields 。