Multi-table inheritance subclasses proxy deletion is broken

[Simon Charette]

Given the following models

#test_app/models.py
from django.db import models

class A(models.Model):
    pass

class B(A):
    pass

class C(B):
    class Meta:
        proxy = True

Running the following tests fails

#test_app/tests.py
from django.test import TestCase

from .models import *


class SimpleTest(TestCase):

    def test_model_subclass_proxy_deletion(self):
        c = C.objects.create()
        self.assertEqual(1, C.objects.count())
        self.assertEqual(1, B.objects.count())
        self.assertEqual(1, A.objects.count())

        c.delete()
        self.assertEqual(0, C.objects.count())
        self.assertEqual(0, B.objects.count())
        self.assertEqual(0, A.objects.count())

    def test_model_subclass_deletion(self):
        b = B.objects.create()
        self.assertEqual(1, C.objects.count())
        self.assertEqual(1, B.objects.count())
        self.assertEqual(1, A.objects.count())

        b.delete()
        self.assertEqual(0, C.objects.count())
        self.assertEqual(0, B.objects.count())
        self.assertEqual(0, A.objects.count())

simon@simon-laptop:~/Bureau/test_deletion$ ./manage.py test test_app 
Creating test database for alias 'default'...
.F
======================================================================
FAIL: test_model_subclass_proxy_deletion (test_app.tests.SimpleTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/simon/Bureau/test_deletion/test_app/tests.py", line 27, in test_model_subclass_proxy_deletion
    self.assertEqual(0, A.objects.count())
AssertionError: 0 != 1

----------------------------------------------------------------------
Ran 2 tests in 0.014s

FAILED (failures=1)
Destroying test database for alias 'default'...

Deleting a multi-table inherited model proxy do not delete all related parent instances while doing it on the concrete model works perfectly.

[Simon Charette]

Failing testcase incorporated into django's test suite

[Simon Charette]

Attached a patch that fixes the issue but change the way pre_delete and post_delete signals are sent.

Before patch only the ConcreteModelSubclassProxy's signals we're sent which was definitely buggy.

When the patch is applied ConcreteModelSubclassProxy's and then ConcreteModel's signals are sent which is still buggy but better IMHO.

In this particular case I beleive signals for the three classes should be triggered in this order: ConcreteModelSubclassProxy then ConcreteModelSubclass and finally ConcreteModel. But that’s another story, as suggested by @carljm I'll open a new ticket that depends on this one and attempt to fix the signal issue there.

I'm also exceptionally marking as Accepted my own bug because I had agreement it's a valid bug on IRC.

[Carl Meyer]

In [17887]:

Fixed #18083 -- Fixed cascade deletion with proxy model of concrete subclass. Thanks Simon Charette for report and patch.

[Simon Charette]

The signal issue ticket is #18094.