Fixed #23076, #25505 -- Fixed deletion of intermediate proxy models.

Thanks to James Murty for his work on an alternate patch.

django/db/models/deletion.py

@@ -55,7 +55,7 @@ def get_candidate_relations_to_delete(opts):
     # The candidate relations are the ones that come from N-1 and 1-1 relations.
     # N-N  (i.e., many-to-many) relations aren't candidates for deletion.
     return (
-        f for f in opts.get_fields(include_hidden=True)
+        f for f in opts.concrete_model._meta.get_fields(include_hidden=True)
         if f.auto_created and not f.concrete and (f.one_to_one or f.one_to_many)
     )
 

tests/proxy_model_inheritance/models.py

@@ -6,7 +6,12 @@ class ConcreteModel(models.Model):
     pass
 
 
-class ConcreteModelSubclass(ConcreteModel):
+class ProxyModel(ConcreteModel):
+    class Meta:
+        proxy = True
+
+
+class ConcreteModelSubclass(ProxyModel):
     pass
 
 

tests/proxy_model_inheritance/tests.py

@@ -9,6 +9,7 @@ from django.utils._os import upath
 
 from .models import (
     ConcreteModel, ConcreteModelSubclass, ConcreteModelSubclassProxy,
+    ProxyModel,
 )
 
 
@@ -43,3 +44,10 @@ class MultiTableInheritanceProxyTest(TestCase):
         self.assertEqual(0, ConcreteModelSubclassProxy.objects.count())
         self.assertEqual(0, ConcreteModelSubclass.objects.count())
         self.assertEqual(0, ConcreteModel.objects.count())
+
+    def test_deletion_through_intermediate_proxy(self):
+        child = ConcreteModelSubclass.objects.create()
+        proxy = ProxyModel.objects.get(pk=child.pk)
+        proxy.delete()
+        self.assertFalse(ConcreteModel.objects.exists())
+        self.assertFalse(ConcreteModelSubclass.objects.exists())