在 MongoEngine 中实现双向关系

发布于 2024-09-26 21:38:23 字数 962 浏览 10 评论 0原文

我正在构建一个使用 MongoDB 和 MongoEngine 来存储数据的 Django 应用程序。为了呈现我的问题的简化版本，假设我想要两个类：User 和 Page。每个页面都应该与一个用户关联，每个用户一个页面。

from mongoengine import *

class Page(Document):
    pass

class User(Document):
    name = StringField()
    page = ReferenceField(Page)

class Page(Document):
    content = StringField()
    user = ReferenceField(User)

（请注意，Page 必须在 User 之前定义。如果我缺少处理循环依赖关系的 Pythonic 方法，请告诉我。）每个文档都可以很好地创建和保存，但将 Page 分配给 User 会引发错误。

u = User(name='Jeff')
u.save()
p = Page(content="I'm a page!")
p.save()
p.user = u
p.save()
u.page = p
u.save()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "build\bdist.win32\egg\mongoengine\document.py", line 71, in save
  File "build\bdist.win32\egg\mongoengine\base.py", line 303, in validate
mongoengine.base.ValidationError: Invalid value for field of type "ReferenceField"

谁能解释为什么会抛出这个异常，我做错了什么，以及如何避免它？

原文

I'm building a Django application that uses MongoDB and MongoEngine to store data. To present a simplified version of my problem, say I want to have two classes: User and Page. Each page should associate itself with a user and each user a page.

from mongoengine import *

class Page(Document):
    pass

class User(Document):
    name = StringField()
    page = ReferenceField(Page)

class Page(Document):
    content = StringField()
    user = ReferenceField(User)

(Note that Page must be defined before User. If I am missing a Pythonic way to handle circular dependencies, let me know.) Each document can be created and saved just fine, but assigning a Page to a User throws an error.

u = User(name='Jeff')
u.save()
p = Page(content="I'm a page!")
p.save()
p.user = u
p.save()
u.page = p
u.save()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "build\bdist.win32\egg\mongoengine\document.py", line 71, in save
  File "build\bdist.win32\egg\mongoengine\base.py", line 303, in validate
mongoengine.base.ValidationError: Invalid value for field of type "ReferenceField"

Can anyone explain why this exception is being thrown, what I am doing wrong, and how I can avoid it?

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就此别过 2024-10-03 21:38:23

这是正确的解决方案：

from mongoengine import *

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

class Page(Document):
    content = StringField()
    user = ReferenceField(User)

使用单引号（'Page'）来表示尚未定义的类。

This is the proper solution:

from mongoengine import *

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

class Page(Document):
    content = StringField()
    user = ReferenceField(User)

Use single quotes ('Page') to denote classes that have not yet been defined.

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音栖息无 2024-10-03 21:38:23

在这种情况下，德鲁的答案是最好的方法，但我想提一下，您也可以使用 GenereicReferenceField：

from mongoengine import *

class User(Document):
    name = StringField()
    page = GenericReferenceField()

class Page(Document):
    content = StringField()
    user = ReferenceField(User)

但同样，对于您的具体问题，请将类名放在单引号中。

Drew's answer is the best way in this case, but I wanted to mention that you can also use a GenereicReferenceField:

from mongoengine import *

class User(Document):
    name = StringField()
    page = GenericReferenceField()

class Page(Document):
    content = StringField()
    user = ReferenceField(User)

But again, for your specific problem, go with the class name in single quotes.

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