mongoengine.errors.ValidationError: A ReferenceField only accepts DBRef or documents

[dmitry-saritasa]

python 2.7.8, latest mongoengine.zip from master:
mongoengine/fields.py, line 990

def validate(self, value):
        if not isinstance(value, (self.document_type, DBRef)):
            self.error("A ReferenceField only accepts DBRef or documents")

        if isinstance(value, Document) and value.id is None:
            self.error('You can only reference documents once they have been '
                       'saved to the database')

first "if" gives the following code

    s = Shift.objects.get(id='554ad0c18a5da50025b7c7c3')
    print s.guard.fname
    #guard = Guard.objects.get(id='55355d7083ba88e23f8b4569')
    guard = Guard.objects.get(id='54d4361183ba88c24a8b4567')
    print guard.fullname
    s.guard = guard
    s.save()

mongoengine.errors.ValidationError: A ReferenceField only accepts DBRef or documents

traceback:
https://gist.github.com/saritasa/27d82f33e3cc33afe1cb

If I run it again - everything works. If I uncomment the first guard and comment 2nd guard, I get this error again. Run 4th time - and error gone.

value is ObjectId type, when I debug code.

Sample data:

{
    "_id" : ObjectId("554ad0c18a5da50025b7c7c3"),
    "parent" : ObjectId("55241c448a5da5002616ede5"),
    "type" : "reassignment",
    "date" : ISODate("2015-05-15T00:00:00.000Z"),
    "school" : ObjectId("55241a8983ba889a678b4567"),
    "location" : ObjectId("55241ae583ba88d46c8b4567"),
    "guard" : ObjectId("54d4361183ba88c24a8b4567"),
    "name" : "1st shift",
    "weekday" : 5,
    "start" : "08:00:00",
    "finish" : "08:30:00",
    "start_sec" : 28800,
    "finish_sec" : 30600,
    "weight" : 28800,
    "holidays" : [],
    "created_at" : ISODate("2015-05-07T02:41:05.618Z"),
    "updated_at" : ISODate("2015-05-11T10:01:58.139Z"),
    "guard_name" : "Guard2Vadik alt Kuz",
    "school_name" : "VictorHigh",
    "location_name" : "Joslin / Gard",
    "guard_phone" : "1231231234",
    "parent_cache" : {
        "_id" : ObjectId("55241c448a5da5002616ede5"),
        "finish" : "08:30:00",
        "weight" : 28800,
        "start_sec" : 28800,
        "finish_sec" : 30600,
        "start" : "08:00:00",
        "guard" : ObjectId("552411f883ba8842658b4567"),
        "type" : "regular"
    }
}

Full shift class is here:
https://gist.github.com/saritasa/ad9387a1259141db4a04

any ideas?

[MRigal]

Not really, but this doesn't sound good... There is quite a bit to do here, but if I have time, I may inspect that further. Else, feel free to submit a PR, at least with a proper (failing) test, even better with the fix :-)

[arnaudriegert]

I had a similar problem and apparently it occurs when the ReferenceField's document class is abstract.

In my case, inside the ReferenceField.validate method, type(value) was myapp.mymodule.documents.subclassmodule.FooBar while self.document_type was myapp.mymodule.documents..Bar (there were actually two dots between documents and Bar).

FooBar is a subclass of Bar (more precisely, it was declared as FooBar(FooBarSerializer, Bar):), but isinstance(value, self.document_type) evaluated to False (so did issubclass(type(value), self.document_type) although I believe that's exactly equivalent).

Hope this helps.

[rahulrameshan]

try using
s.guard = guard..to_dbref()
s.save()

[0xWilliamWang]

@rahulrameshan you are right, thank you.

[letoss]

Mongoengine version: 0.23.1
Hello, I arrived at this issue after dealing with the same. I actually realized that there are two ways on solving it.

This one returns an ObjectId

guard = Guard.objects.get(id='54d4361183ba88c24a8b4567')
s.guard = guard.id
s.save()

In case you already have the guard ID, you don't need to retrieve the instance from the DB, you could just do:

from bson.objectid import ObjectId
g.guard = ObjectId('54d4361183ba88c24a8b4567')
s.save()