Use of proxy models broke polymorphic / some bad ctypes resulted in no results at all

[rrauenza]

django-polymorphic 2.0.2, django 1.11.15

I came across an issue I wanted to make sure you're aware of -- I'm no longer using proxy models, so this is not affecting me currently.

Let's assume

class Parent(Model): 
   pass

Child(Parent): 
   pass

When using proxy models, the polymorphic ctype of a proxy of Child ended up making a new contenttype for ProxyChild in the django_contenttypes and pointing the Parent.polymorphic_ctype to it.

Now ... I was trying to generate these proxies dynamically, so that could be an issue, i.e.,

# From memory ... I think this is how I did it.  Code is gone now.
def _proxy(cls):
    class Meta:
        proxy = True
    p = type("%sProxy" % cls.__name__, cls, dict(Meta=Meta)
    p.save = ...  # I was overriding save on a bunch of these temporarily.
    return p

ChildProxy = _proxy(Child)

I see here you seem to actually check ._meta for proxy, so perhaps this is just an issue with Meta not being properly created above.

....but this caused a secondary issue which took me a while to figure out. Since some ctype's were invalid, Child.objects.all() would return an empty queryset. Yet I could do Child.objects.get(id=xxx) for some objects. After wiping the db (it was dev instance), I later realized the root cause is possibly that Polymorphic is trying to (pre?)resolve all of the ctypes.

I'm wondering if this is the desired behavior -- I feel like polymorphic should instead either throw an exception when encountering bad ctypes, or it should ignore those instances. Instead it appeared to ignore even the proper ones.

I can put some effort into trying to reproduce this ... but would like the project's thoughts first. I think we can probably assume since I see proxy code in the code base that my dynamic proxy generation is the root issue. And we can ignore that ...

But do you know of any reasons why a couple of bad ctypes in Parent's table would make Child.objects.all() return nothing when there are some good entries still?

[bckohan]

#676