#25361: Unpickling of QuerySet fails in presence of abstract intermediate model
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Reporter: bronger | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Consider the following model hierarchy:
{{{
from django.db import models
class Pizza(models.Model):
timestamp = models.DateTimeField("last modified", auto_now=True)
class SpecialPizza(Pizza):
class Meta:
abstract = True
ordering = ["timestamp"]
class MyPizza(SpecialPizza):
pass
class Topping(models.Model):
pizza = models.ForeignKey(MyPizza, related_name="toppings")
class Meta:
ordering = ["pizza"]
}}}
QuerySet objects containing MyPizza objects with Toppings cannot be
pickled and unpickled:
{{{
my_pizza = models.MyPizza.objects.create()
my_pizza.toppings.add(models.Topping())
pickled = pickle.dumps(my_pizza.toppings.all())
response = pickle.loads(pickled)
}}}
The traceback is:
{{{
Traceback:
File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py"
in get_response
132. response = wrapped_callback(request,
*callback_args, **callback_kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py"
in inner
145. return func(*args, **kwargs)
File "/tmp/myproject/myproject/myapp/views.py" in test
9. response = pickle.loads(pickled)
File "/usr/lib/python2.7/pickle.py" in loads
1383. return Unpickler(file).load()
File "/usr/lib/python2.7/pickle.py" in load
858. dispatch[key](self)
File "/usr/lib/python2.7/pickle.py" in load_reduce
1134. value = func(*args)
File "/usr/local/lib/python2.7/dist-
packages/django/db/models/fields/__init__.py" in _load_field
66. return apps.get_model(app_label,
model_name)._meta.get_field(field_name)
File "/usr/local/lib/python2.7/dist-packages/django/apps/registry.py" in
get_model
202. return
self.get_app_config(app_label).get_model(model_name.lower())
File "/usr/local/lib/python2.7/dist-packages/django/apps/config.py" in
get_model
162. "App '%s' doesn't have a '%s' model." %
(self.label, model_name))
Exception Type: LookupError at /
Exception Value: App 'myapp' doesn't have a 'specialpizza' model.
}}}
If one removes one of the "ordering" fields, the unpickler uses "MyPizza"
instead of "SpecialPizza", which is correct and should always be the case.
--
Ticket URL: <https://code.djangoproject.com/ticket/25361>
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