python - Implementing Bi-Directional relationships in MongoEngine -

i'm building django application uses mongodb , mongoengine store data. present simplified version of problem, want have 2 classes: user , page. each page should associate user , each user 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 page must defined before user. if missing pythonic way handle circular dependencies, let me know.) each document can created , saved fine, assigning page user throws error.

u = user(name='jeff') u.save() p = page(content="i'm 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 field of type "referencefield" 

can explain why exception being thrown, doing wrong, , how can avoid it?

this 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') denote classes have not yet been defined.