Pymodm: ImportError (Two models referencing each other)

Question

I'm writing a todo app using flask and mongoDB and Pymodm as an ODM. I have two models named User and UserGroups. these two reference each other like so:

user.py

from api.models.userGroup import group
class User(MongoModel):
   _id    = fields.IntegerField(primary_key=True)
   email  = fields.CharField()
   password  = fields.CharField()
   createdAt = fields.DateTimeField(default=datetime.datetime.now())
   groups = [fields.ReferenceField('group')]
   personalTodoLists = fields.EmbeddedDocumentListField('list')

userGroup.py

from api.models.user import user
class UserGroup(MongoModel, EmbeddedMongoModel):
   _id    = fields.IntegerField(primary_key=True)
   name  = fields.CharField()
   createdAt = fields.DateTimeField(default=datetime.datetime.now())
   ownerId = fields.ReferenceField('user')
   contributors = [fields.ReferenceField('user')]
   todoLits = fields.EmbeddedDocumentListField('list')

I'm getting the error: "ImportError: cannot import name 'user'"

How can i make references in this case properly?

Answer 1

Circular reference is a common problem with many-to-many relationships. The usual solution implemented by the packages is to provide you with a way to refer to (yet to be defined) other model using a string with its name, instead of the object itself.

I can see that's what you've done, actually. Eg:

    groups = [fields.ReferenceField('group')]

There should be no need for you to actually import those models, then. Just comment out/remove the offending import lines, and it should work.