PicklingError: Can't pickle User Groups about django-cacheops

[Suor]

Problem here is that you can not pickle an instance of dynamically created class, unless it binded into module namespace as statically created one. Here is a monkey patch workaround:

from django.db.models.fields import related
def patched_create_many_to_many_intermediary_model(field, klass):
    model = original_create_many_to_many_intermediary_model(field, klass)
    setattr(sys.modules[model.__module__], model.__name__, model)
    return model
original_create_many_to_many_intermediary_model = related.create_many_to_many_intermediary_model
related.create_many_to_many_intermediary_model = patched_create_many_to_many_intermediary_model

I'll probably should incorporate it into cacheops install.

[Suor]

The thing is you should apply this patch very early, before any intermediary model classes are created.
I usually add

from django.core.management import setup_environ
setup_environ(settings)
import monkey

just before

execute_manager(settings)

in manage.py. And then write all my monkey patches into monkey.py in the same directory with manage.py

[kevinpostal]

I added your monkey patch and I am still receiving the error. Perhaps its because I am using http://gunicorn.org/ ?

[Suor]

Try opening django shell ./manage.py shell and pickling an instance of any intermidiate model there:

>>> from django.contrib.auth.models import User
>>> g = User._meta.get_field('groups').rel.through.objects.all()[0]
>>> from pickle import dumps
>>> dumps(g)
"cmonkey\nmodel_unpickle\np0\n(cdjango.contrib.auth.models\nUser_groups\np1 ..."

If that does not work check if you are loading django.contrib.auth.models before patch - patch should go berfore.

[Suor]

I didn't use gunicorn, however if it uses separate startup script (not manage.py) you should add the monkey patch there too.

[Suor]

This should be fixed by c413f8b.
Can you confirm that?

[Suor]

Some guys confirmed in other threads.

[michaelmior]

I was wondering if you could help explain more about the nature of the error. I seem to be experiencing a similar issue (same exception value) when pickling a User model with related fields after trying to upgrade to Django 1.5. I'm not using cacheops, but the issue seems similar so any insight you can give would be helpful. Thanks :)