switch_db does not dereference properly

[trein]

I found switch_db functionality really handy and decided to tried it out this weekend. The problem is that it seems ReferenceFields are not properly resolved while in switch_db context. Here is what I've tried so far:

class Agency(DocumentModel):
    agency_id = db.StringField()
    name = db.StringField()
    url = db.StringField()
    timezone = db.StringField()
    lang = db.StringField()
    phone = db.StringField()
    fare_url = db.StringField()

class Route(DocumentModel):
    agency = db.ReferenceField(Agency)
    route_id = db.StringField()
    short_name = db.StringField()
    long_name = db.StringField()
    route_type = db.StringField()
    desc = db.StringField()
    url = db.StringField()
    color = db.StringField()
    text_color = db.StringField()

def route(self, route_id):
    with switch_db(document_models.Route, self.db_name()) as Route:
        route = Route.objects.get(route_id=route_id)
        assert (isinstance(route.agency, document_models.Agency))
        return route

The assertion fails as route.agency returns a Dbref. However, if I remove completely swith_db and setup the initial database as self.db_name(), everything works as expected.

def route(self, route_id):
    route = document_models.Route.objects.get(route_id=route_id)
    assert (isinstance(route.agency, document_models.Agency))
    return route

I even tried several other cases, with and without select_related(). No luck.

[trein]

Apparently that's not the focus of MongoEngine. I just don't understand why it provides a feature such as switch_db when it does not work properly with dereferencing. Please, correct me if I'm wrong, but the main reason people use MongoEngine is because of dereferencing. Otherwise, the use of straight up PyMongo would be a more suitable option I suppose.