[1.5.x] Fixed #19720 -- Oracle ordering related delete regression

When a query had a complex where condition (a condition targeting more
than the base table) a subquery was used for deletion. However, the
query had default ordering from the model's meta and Oracle doesn't
work with ordered subqueries.

The regression was caused by fast-path deletion code introduced in
1cd6e04cd4f768bcd4385b75de433d497d938f82 for fixing #18676.

Thanks to Dylan Klomparens for the report.

Backpatch of 8ef3235034a1a7616714a5d61486dc68536f74ee

3 files changed, 23 insertions, 2 deletions

diff --git a/django/db/models/query.py b/django/db/models/query.py
index 6b628e81cb..952739e939 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -530,7 +530,7 @@ class QuerySet(object):
         # Disable non-supported fields.
         del_query.query.select_for_update = False
         del_query.query.select_related = False
-        del_query.query.clear_ordering()
+        del_query.query.clear_ordering(force_empty=True)
 
         collector = Collector(using=del_query.db)
         collector.collect(del_query)
diff --git a/tests/regressiontests/delete_regress/models.py b/tests/regressiontests/delete_regress/models.py
index dbe383fb41..3632a7dbc1 100644
--- a/tests/regressiontests/delete_regress/models.py
+++ b/tests/regressiontests/delete_regress/models.py
@@ -99,3 +99,13 @@ class OrgUnit(models.Model):
 class Login(models.Model):
     description = models.CharField(max_length=32)
     orgunit = models.ForeignKey(OrgUnit)
+
+class House(models.Model):
+    address = models.CharField(max_length=32)
+
+class OrderedPerson(models.Model):
+    name = models.CharField(max_length=32)
+    lives_in = models.ForeignKey(House)
+
+    class Meta:
+        ordering = ['name']
diff --git a/tests/regressiontests/delete_regress/tests.py b/tests/regressiontests/delete_regress/tests.py
index f94bb2f20c..1bc4e781fe 100644
--- a/tests/regressiontests/delete_regress/tests.py
+++ b/tests/regressiontests/delete_regress/tests.py
@@ -9,7 +9,7 @@ from django.test import TestCase, TransactionTestCase, skipUnlessDBFeature
 from .models import (Book, Award, AwardNote, Person, Child, Toy, PlayedWith,
     PlayedWithNote, Email, Researcher, Food, Eaten, Policy, Version, Location,
     Item, Image, File, Photo, FooFile, FooImage, FooPhoto, FooFileProxy, Login,
-    OrgUnit)
+    OrgUnit, OrderedPerson, House)
 
 
 # Can't run this test under SQLite, because you can't
@@ -355,3 +355,14 @@ class Ticket19102Tests(TestCase):
         self.assertFalse(Login.objects.filter(pk=self.l1.pk).exists())
         self.assertTrue(Login.objects.filter(pk=self.l2.pk).exists())
 
+
+class OrderedDeleteTests(TestCase):
+    def test_meta_ordered_delete(self):
+        # When a subquery is performed by deletion code, the subquery must be
+        # cleared of all ordering. There was a but that caused _meta ordering
+        # to be used. Refs #19720.
+        h = House.objects.create(address='Foo')
+        OrderedPerson.objects.create(name='Jack', lives_in=h)
+        OrderedPerson.objects.create(name='Bob', lives_in=h)
+        OrderedPerson.objects.filter(lives_in__address='Foo').delete()
+        self.assertEqual(OrderedPerson.objects.count(), 0)