CachedReferenceField creates DBRefs on to_python, but can't save them on to_mongo

[amitlicht]

import mongoengine
from mongoengine import Document
from mongoengine.fields import CachedReferenceField, BooleanField, IntField

mongoengine.connect('test')

class TestCachedDoc(Document):
    test = BooleanField(required=True)

class TestDoc(Document):
    cached_doc = CachedReferenceField(TestCachedDoc)
    other_field = IntField(required=True)

TestDoc.objects.delete()
TestDoc(cached_doc=TestCachedDoc(test=False).save(),
        other_field=10).save()
t = TestDoc.objects.get()
t.other_field = 1
t.save()   # --> raises mongoengine.errors.ValidationError: ValidationError (TestDoc:559003e21bacb5bcf87a3195) (A CachedReferenceField only accepts documents: ['cached_doc'])

[coffenbacher]

Queryset evaluation performance for me after this change is horrendous, unfortunately...

Item.objects.all() on 200 items with a few CachedReferenceFields apiece takes ~10 seconds to dereference everything before returning. It's not lazy, either, which makes this untenable for my uses at the moment.

I'm not 100% sure what the original design of CachedReferenceField called for, but this works perfectly for my use case and is highly performant since it's using the cached values:

def to_python(self, value):
    if isinstance(value, dict):
        return self.document_type._from_son(value)
    return value

[MRigal]

You're right @coffenbacher , we should add this. Are you or @amitlicht willing to submit a complementary PR?

[yarneo]

There are so many issues with CachedReferenceFields that it baffles me how it was put in the version to begin with. Basically unworkable, you can't fetch the object then save it without a validation error. You can't append a cachedreferencefield to a list without an attribute error. I would suggest to remove it entirely to not cause developers extra headache.

[coffenbacher]

I ended up abandoning CachedReferenceField and completing my project using a different approach, so unfortunately I'm not in a position to submit a PR on this one