Fixed #23460 -- Added literal `%s` support to extra() QuerySets.

django/db/models/sql/query.py

@@ -1775,6 +1775,7 @@ class Query(object):
                 entry_params = []
                 pos = entry.find("%s")
                 while pos != -1:
+                    if pos == 0 or entry[pos - 1] != '%':
                         entry_params.append(next(param_iter))
                     pos = entry.find("%s", pos + 2)
                 select_pairs[name] = (entry, entry_params)

docs/ref/models/querysets.txt

@@ -1144,11 +1144,12 @@ of the arguments is required, but you should use at least one of them.
           select=OrderedDict([('a', '%s'), ('b', '%s')]),
           select_params=('one', 'two'))
 
-  The only thing to be careful about when using select parameters in
-  ``extra()`` is to avoid using the substring ``"%%s"`` (that's *two*
-  percent characters before the ``s``) in the select strings. Django's
-  tracking of parameters looks for ``%s`` and an escaped ``%`` character
-  like this isn't detected. That will lead to incorrect results.
+  If you need to use a literal ``%s`` inside your select string, use
+  the sequence ``%%s``.
+
+  .. versionchanged:: 1.8
+
+      Prior to 1.8, you were unable to escape a literal ``%s``.
 
 * ``where`` / ``tables``
 

docs/releases/1.8.txt

@@ -281,6 +281,9 @@ Models
   Django uses whenever objects are loaded using the ORM. The method allows
   customizing model loading behavior.
 
+* ``extra(select={...})`` now allows you to escape a literal ``%s`` sequence
+  using ``%%s``.
+
 Signals
 ^^^^^^^
 

tests/queries/tests.py

@@ -1655,6 +1655,21 @@ class Queries5Tests(TestCase):
             ['<Note: n1>', '<Note: n2>']
         )
 
+    def test_extra_select_literal_percent_s(self):
+        # Allow %%s to escape select clauses
+        self.assertEqual(
+            Note.objects.extra(select={'foo': "'%%s'"})[0].foo,
+            '%s'
+        )
+        self.assertEqual(
+            Note.objects.extra(select={'foo': "'%%s bar %%s'"})[0].foo,
+            '%s bar %s'
+        )
+        self.assertEqual(
+            Note.objects.extra(select={'foo': "'bar %%s'"})[0].foo,
+            'bar %s'
+        )
+
 
 class SelectRelatedTests(TestCase):
     def test_tickets_3045_3288(self):