Fix proxy model Query.remove_inherited_models()

Fixed #18248 -- proxy models were added to included_inherited_models
in sql.query.Query. The variable is meant to be used for multitable
inheritance only. This mistake caused problems in situations where
proxy model's query was reused.

django/db/models/sql/compiler.py

@@ -261,12 +261,12 @@ class SQLCompiler(object):
         result = []
         if opts is None:
             opts = self.query.model._meta
+        # Skip all proxy to the root proxied model
+        opts = opts.concrete_model._meta
         qn = self.quote_name_unless_alias
         qn2 = self.connection.ops.quote_name
         aliases = set()
         only_load = self.deferred_to_columns()
-        # Skip all proxy to the root proxied model
-        proxied_model = opts.concrete_model
 
         if start_alias:
             seen = {None: start_alias}
@@ -277,12 +277,9 @@ class SQLCompiler(object):
                 try:
                     alias = seen[model]
                 except KeyError:
-                    if model is proxied_model:
-                        alias = start_alias
-                    else:
-                        link_field = opts.get_ancestor_link(model)
-                        alias = self.query.join((start_alias, model._meta.db_table,
-                                link_field.column, model._meta.pk.column))
+                    link_field = opts.get_ancestor_link(model)
+                    alias = self.query.join((start_alias, model._meta.db_table,
+                            link_field.column, model._meta.pk.column))
                     seen[model] = alias
             else:
                 # If we're starting from the base model of the queryset, the

django/db/models/sql/query.py

@@ -933,21 +933,16 @@ class Query(object):
         whereas column determination is a later part, and side-effect, of
         as_sql()).
         """
-        opts = self.model._meta
+        # Skip all proxy models
+        opts = self.model._meta.concrete_model._meta
         root_alias = self.tables[0]
         seen = {None: root_alias}
 
-        # Skip all proxy to the root proxied model
-        proxied_model = opts.concrete_model
-
         for field, model in opts.get_fields_with_model():
             if model not in seen:
-                if model is proxied_model:
-                    seen[model] = root_alias
-                else:
-                    link_field = opts.get_ancestor_link(model)
-                    seen[model] = self.join((root_alias, model._meta.db_table,
-                            link_field.column, model._meta.pk.column))
+                link_field = opts.get_ancestor_link(model)
+                seen[model] = self.join((root_alias, model._meta.db_table,
+                        link_field.column, model._meta.pk.column))
         self.included_inherited_models = seen
 
     def remove_inherited_models(self):

tests/regressiontests/queries/models.py

@@ -10,6 +10,10 @@ from django.db import models
 class DumbCategory(models.Model):
     pass
 
+class ProxyCategory(DumbCategory):
+    class Meta:
+        proxy = True
+
 class NamedCategory(DumbCategory):
     name = models.CharField(max_length=10)
 

tests/regressiontests/queries/tests.py

@@ -19,7 +19,7 @@ from .models import (Annotation, Article, Author, Celebrity, Child, Cover,
     ManagedModel, Member, NamedCategory, Note, Number, Plaything, PointerA,
     Ranking, Related, Report, ReservedName, Tag, TvChef, Valid, X, Food, Eaten,
     Node, ObjectA, ObjectB, ObjectC, CategoryItem, SimpleCategory,
-    SpecialCategory, OneToOneCategory, NullableName)
+    SpecialCategory, OneToOneCategory, NullableName, ProxyCategory)
 
 
 class BaseQuerysetTest(TestCase):
@@ -1952,3 +1952,15 @@ class EmptyStringsAsNullTest(TestCase):
             DumbCategory.objects.exclude(namedcategory__name__in=['nonexisting']),
             [self.nc.pk], attrgetter('pk')
         )
+
+class ProxyQueryCleanupTest(TestCase):
+    def test_evaluated_proxy_count(self):
+        """
+        Test that generating the query string doesn't alter the query's state
+        in irreversible ways. Refs #18248.
+        """
+        ProxyCategory.objects.create()
+        qs = ProxyCategory.objects.all()
+        self.assertEqual(qs.count(), 1)
+        str(qs.query)
+        self.assertEqual(qs.count(), 1)