From 9319dc496c5f8d215a293fff5fb974e48e68454d Mon Sep 17 00:00:00 2001
From: Malcolm Tredinnick <malcolm.tredinnick@gmail.com>
Date: Fri, 24 Oct 2008 06:09:47 +0000
Subject: [PATCH] Fixed #9406 -- Ensure that each database column is only
 represented once in the "ORDER BY" clause of an SQL statement.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9251 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/db/models/sql/query.py                 | 24 +++++++++++++------
 .../model_inheritance_regress/models.py       | 10 ++++++++
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 01fbd3d002..ee63a0214f 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -621,6 +621,12 @@ class Query(object):
             asc, desc = ORDER_DIR['ASC']
         else:
             asc, desc = ORDER_DIR['DESC']
+
+        # It's possible, due to model inheritance, that normal usage might try
+        # to include the same field more than once in the ordering. We track
+        # the table/column pairs we use and discard any after the first use.
+        processed_pairs = set()
+
         for field in ordering:
             if field == '?':
                 result.append(self.connection.ops.random_function_sql())
@@ -638,18 +644,22 @@ class Query(object):
                 # on verbatim.
                 col, order = get_order_dir(field, asc)
                 table, col = col.split('.', 1)
-                elt = '%s.%s' % (qn(table), col)
-                if not distinct or elt in select_aliases:
-                    result.append('%s %s' % (elt, order))
+                if (table, col) not in processed_pairs:
+                    elt = '%s.%s' % (qn(table), col)
+                    processed_pairs.add((table, col))
+                    if not distinct or elt in select_aliases:
+                        result.append('%s %s' % (elt, order))
             elif get_order_dir(field)[0] not in self.extra_select:
                 # 'col' is of the form 'field' or 'field1__field2' or
                 # '-field1__field2__field', etc.
                 for table, col, order in self.find_ordering_name(field,
                         self.model._meta, default_order=asc):
-                    elt = '%s.%s' % (qn(table), qn2(col))
-                    if distinct and elt not in select_aliases:
-                        ordering_aliases.append(elt)
-                    result.append('%s %s' % (elt, order))
+                    if (table, col) not in processed_pairs:
+                        elt = '%s.%s' % (qn(table), qn2(col))
+                        processed_pairs.add((table, col))
+                        if distinct and elt not in select_aliases:
+                            ordering_aliases.append(elt)
+                        result.append('%s %s' % (elt, order))
             else:
                 col, order = get_order_dir(field, asc)
                 elt = qn2(col)
diff --git a/tests/regressiontests/model_inheritance_regress/models.py b/tests/regressiontests/model_inheritance_regress/models.py
index 2777d1f23a..06a886e0be 100644
--- a/tests/regressiontests/model_inheritance_regress/models.py
+++ b/tests/regressiontests/model_inheritance_regress/models.py
@@ -257,4 +257,14 @@ DoesNotExist: ArticleWithAuthor matching query does not exist.
 # without error.
 >>> _ = QualityControl.objects.create(headline="Problems in Django", pub_date=datetime.datetime.now(), quality=10, assignee="adrian")
 
+# Ordering should not include any database column more than once (this is most
+# likely to ocurr naturally with model inheritance, so we check it here).
+# Regression test for #9390. This necessarily pokes at the SQL string for the
+# query, since the duplicate problems are only apparent at that late stage.
+>>> sql = ArticleWithAuthor.objects.order_by('pub_date', 'pk').query.as_sql()[0]
+>>> fragment = sql[sql.find('ORDER BY'):]
+>>> pos = fragment.find('pub_date')
+>>> fragment.find('pub_date', pos + 1) == -1
+True
+
 """}