Fixed #12328 -- Corrected the handling of subqueries with ordering and slicing, especially when used in delete subqueries. Thanks to Walter Doekes for the report.

This fixes a feature that isn't available under MySQL and Oracle (Refs #10099).

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12912 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/__init__.py

@@ -95,6 +95,7 @@ class BaseDatabaseFeatures(object):
     # If True, don't use integer foreign keys referring to, e.g., positive
     # integer primary keys.
     related_fields_match_type = False
+    allow_sliced_subqueries = True
 
 class BaseDatabaseOperations(object):
     """

django/db/backends/mysql/base.py

@@ -123,6 +123,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     update_can_self_select = False
     allows_group_by_pk = True
     related_fields_match_type = True
+    allow_sliced_subqueries = False
 
 class DatabaseOperations(BaseDatabaseOperations):
     compiler_module = "django.db.backends.mysql.compiler"

django/db/backends/oracle/base.py

@@ -52,6 +52,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     interprets_empty_strings_as_nulls = True
     uses_savepoints = True
     can_return_id_from_insert = True
+    allow_sliced_subqueries = False
 
 
 class DatabaseOperations(BaseDatabaseOperations):

django/db/models/query.py

@@ -3,6 +3,7 @@ The main QuerySet implementation. This provides the public API for the ORM.
 """
 
 from copy import deepcopy
+from itertools import izip
 
 from django.db import connections, router, transaction, IntegrityError
 from django.db.models.aggregates import Aggregate
@@ -429,11 +430,13 @@ class QuerySet(object):
         # becoming too long.
         seen_objs = None
         while 1:
-            # Collect all the objects to be deleted in this chunk, and all the
+            # Collect a chunk of objects to be deleted, and then all the
             # objects that are related to the objects that are to be deleted.
+            # The chunking *isn't* done by slicing the del_query because we
+            # need to maintain the query cache on del_query (see #12328)
             seen_objs = CollectedObjects(seen_objs)
-            for object in del_query[:CHUNK_SIZE]:
-                object._collect_sub_objects(seen_objs)
+            for i, obj in izip(xrange(CHUNK_SIZE), del_query):
+                obj._collect_sub_objects(seen_objs)
 
             if not seen_objs:
                 break

django/db/models/sql/compiler.py

@@ -120,12 +120,14 @@ class SQLCompiler(object):
         """
         Perform the same functionality as the as_sql() method, returning an
         SQL string and parameters. However, the alias prefixes are bumped
-        beforehand (in a copy -- the current query isn't changed) and any
-        ordering is removed.
+        beforehand (in a copy -- the current query isn't changed), and any
+        ordering is removed if the query is unsliced.
 
         Used when nesting this query inside another.
         """
         obj = self.query.clone()
+        if obj.low_mark == 0 and obj.high_mark is None:
+            # If there is no slicing in use, then we can safely drop all ordering
             obj.clear_ordering(True)
         obj.bump_prefix()
         return obj.get_compiler(connection=self.connection).as_sql()

tests/regressiontests/queries/tests.py

@@ -1,6 +1,10 @@
 import unittest
-from models import Tag, Annotation
+
+from django.db import DatabaseError, connections, DEFAULT_DB_ALIAS
 from django.db.models import Count
+from django.test import TestCase
+
+from models import Tag, Annotation, DumbCategory
 
 class QuerysetOrderedTests(unittest.TestCase):
     """
@@ -25,3 +29,37 @@ class QuerysetOrderedTests(unittest.TestCase):
         self.assertEqual(qs.ordered, False)
         self.assertEqual(qs.order_by('num_notes').ordered, True)
 
+
+class SubqueryTests(TestCase):
+    def setUp(self):
+        DumbCategory.objects.create(id=1)
+        DumbCategory.objects.create(id=2)
+        DumbCategory.objects.create(id=3)
+
+    def test_ordered_subselect(self):
+        "Subselects honor any manual ordering"
+        try:
+            query = DumbCategory.objects.filter(id__in=DumbCategory.objects.order_by('-id')[0:2])
+            self.assertEquals(set(query.values_list('id', flat=True)), set([2,3]))
+
+            query = DumbCategory.objects.filter(id__in=DumbCategory.objects.order_by('-id')[:2])
+            self.assertEquals(set(query.values_list('id', flat=True)), set([2,3]))
+
+            query = DumbCategory.objects.filter(id__in=DumbCategory.objects.order_by('-id')[2:])
+            self.assertEquals(set(query.values_list('id', flat=True)), set([1]))
+        except DatabaseError:
+            # Oracle and MySQL both have problems with sliced subselects.
+            # This prevents us from even evaluating this test case at all.
+            # Refs #10099
+            self.assertFalse(connections[DEFAULT_DB_ALIAS].features.allow_sliced_subqueries)
+
+    def test_sliced_delete(self):
+        "Delete queries can safely contain sliced subqueries"
+        try:
+            DumbCategory.objects.filter(id__in=DumbCategory.objects.order_by('-id')[0:1]).delete()
+            self.assertEquals(set(DumbCategory.objects.values_list('id', flat=True)), set([1,2]))
+        except DatabaseError:
+            # Oracle and MySQL both have problems with sliced subselects.
+            # This prevents us from even evaluating this test case at all.
+            # Refs #10099
+            self.assertFalse(connections[DEFAULT_DB_ALIAS].features.allow_sliced_subqueries)