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.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15726 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 13 insertions, 5 deletions

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 341765c608..8fa3419059 100644
--- a/django/db/models/sql/query.py
+++ b/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.