Metaclass error from Flask-MongoKit

Question

I'm trying to assemble a basic login system using Flask, Flask-Login, and Flask-MongoKit.

Here's my User class:

class User(Document):
    __collection__ = 'users'
    structure = {
        'username': basestring,
        'password': basestring,
        'date_created': datetime
    }
    required_fields = ['username', 'password']
    default_values = {
        'date_created': datetime.utcnow
    }

When I connect the Document model to the database (db.register([User])), querying against the document (db.User.one({'username': form.username})) gives me this lovely error:

TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

I don't understand this error at all, and I have no idea how to fix it. What's going wrong?

NOTE: I understand what a metaclass conflict is. What I don't see is how I've caused one: it seems to be triggered somewhere inside MongoKit.

Answer 1

The problem turned out to be that I was importing the class wrong (I was feeding the parent module to db.register instead of the class.