[1.2.X] Fixed #12252 -- Ensure that queryset unions are commutative. Thanks to benreynwar for the report, and draft patch, and to Karen and Ramiro for the review eyeballs and patch updates.

Backport of r15726 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15727 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -446,6 +446,8 @@ class Query(object):
             "Cannot combine a unique query with a non-unique query."
 
         self.remove_inherited_models()
+        l_tables = set([a for a in self.tables if self.alias_refcount[a]])
+        r_tables = set([a for a in rhs.tables if rhs.alias_refcount[a]])
         # Work out how to relabel the rhs aliases, if necessary.
         change_map = {}
         used = set()
@@ -463,13 +465,19 @@ class Query(object):
             first = False
 
         # So that we don't exclude valid results in an "or" query combination,
-        # the first join that is exclusive to the lhs (self) must be converted
+        # all joins exclusive to either the lhs or the rhs must be converted
         # to an outer join.
         if not conjunction:
-            for alias in self.tables[1:]:
-                if self.alias_refcount[alias] == 1:
-                    self.promote_alias(alias, True)
-                    break
+            # Update r_tables aliases.
+            for alias in change_map:
+                if alias in r_tables:
+                    r_tables.remove(alias)
+                    r_tables.add(change_map[alias])
+            # Find aliases that are exclusive to rhs or lhs.
+            # These are promoted to outer joins.
+            outer_aliases = (l_tables | r_tables) - (l_tables & r_tables)
+            for alias in outer_aliases:
+                self.promote_alias(alias, True)
 
         # Now relabel a copy of the rhs where-clause and add it to the current
         # one.

tests/regressiontests/queries/models.py

@@ -294,3 +294,26 @@ class Node(models.Model):
 
     def __unicode__(self):
         return u"%s" % self.num
+
+# Bug #12252
+class ObjectA(models.Model):
+    name = models.CharField(max_length=50)
+
+    def __unicode__(self):
+        return self.name
+
+class ObjectB(models.Model):
+    name = models.CharField(max_length=50)
+    objecta = models.ForeignKey(ObjectA)
+    number = models.PositiveSmallIntegerField()
+
+    def __unicode__(self):
+        return self.name
+
+class ObjectC(models.Model):
+    name = models.CharField(max_length=50)
+    objecta = models.ForeignKey(ObjectA)
+    objectb = models.ForeignKey(ObjectB)
+
+    def __unicode__(self):
+       return self.name

tests/regressiontests/queries/tests.py

@@ -14,7 +14,8 @@ from django.utils.datastructures import SortedDict
 from models import (Annotation, Article, Author, Celebrity, Child, Cover, Detail,
     DumbCategory, ExtraInfo, Fan, Item, LeafA, LoopX, LoopZ, ManagedModel,
     Member, NamedCategory, Note, Number, Plaything, PointerA, Ranking, Related,
-    Report, ReservedName, Tag, TvChef, Valid, X, Food, Eaten, Node)
+    Report, ReservedName, Tag, TvChef, Valid, X, Food, Eaten, Node, ObjectA, ObjectB,
+    ObjectC)
 
 
 class BaseQuerysetTest(TestCase):
@@ -1566,6 +1567,66 @@ class ToFieldTests(TestCase):
             [node1]
         )
 
+class UnionTests(unittest.TestCase):
+    """
+    Tests for the union of two querysets. Bug #12252.
+    """
+    def setUp(self):
+        objectas = []
+        objectbs = []
+        objectcs = []
+        a_info = ['one', 'two', 'three']
+        for name in a_info:
+            o = ObjectA(name=name)
+            o.save()
+            objectas.append(o)
+        b_info = [('un', 1, objectas[0]), ('deux', 2, objectas[0]), ('trois', 3, objectas[2])]
+        for name, number, objecta in b_info:
+            o = ObjectB(name=name, number=number, objecta=objecta)
+            o.save()
+            objectbs.append(o)
+        c_info = [('ein', objectas[2], objectbs[2]), ('zwei', objectas[1], objectbs[1])]
+        for name, objecta, objectb in c_info:
+            o = ObjectC(name=name, objecta=objecta, objectb=objectb)
+            o.save()
+            objectcs.append(o)
+
+    def check_union(self, model, Q1, Q2):
+        filter = model.objects.filter
+        self.assertEqual(set(filter(Q1) | filter(Q2)), set(filter(Q1 | Q2)))
+        self.assertEqual(set(filter(Q2) | filter(Q1)), set(filter(Q1 | Q2)))
+
+    def test_A_AB(self):
+        Q1 = Q(name='two')
+        Q2 = Q(objectb__name='deux')
+        self.check_union(ObjectA, Q1, Q2)
+
+    def test_A_AB2(self):
+        Q1 = Q(name='two')
+        Q2 = Q(objectb__name='deux', objectb__number=2)
+        self.check_union(ObjectA, Q1, Q2)
+
+    def test_AB_ACB(self):
+        Q1 = Q(objectb__name='deux')
+        Q2 = Q(objectc__objectb__name='deux')
+        self.check_union(ObjectA, Q1, Q2)
+
+    def test_BAB_BAC(self):
+        Q1 = Q(objecta__objectb__name='deux')
+        Q2 = Q(objecta__objectc__name='ein')
+        self.check_union(ObjectB, Q1, Q2)
+
+    def test_BAB_BACB(self):
+        Q1 = Q(objecta__objectb__name='deux')
+        Q2 = Q(objecta__objectc__objectb__name='trois')
+        self.check_union(ObjectB, Q1, Q2)
+
+    def test_BA_BCA__BAB_BAC_BCA(self):
+        Q1 = Q(objecta__name='one', objectc__objecta__name='two')
+        Q2 = Q(objecta__objectc__name='ein', objectc__objecta__name='three', objecta__objectb__name='trois')
+        self.check_union(ObjectB, Q1, Q2)
+
+
 
 # In Python 2.6 beta releases, exceptions raised in __len__ are swallowed
 # (Python issue 1242657), so these cases return an empty list, rather than