Fixed #16809 -- Forced MySQL to behave like a database. This avoids a problem where queries that do IS NONE checks can return the wrong result the first time they are executed if there is a recently inserted row. Thanks to James Pyrich for the debug work and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16785 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/mysql/base.py

@@ -309,7 +309,9 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         return False
 
     def _cursor(self):
+        new_connection = False
         if not self._valid_connection():
+            new_connection = True
             kwargs = {
                 'conv': django_conversions,
                 'charset': 'utf8',
@@ -336,8 +338,14 @@ class DatabaseWrapper(BaseDatabaseWrapper):
             self.connection.encoders[SafeUnicode] = self.connection.encoders[unicode]
             self.connection.encoders[SafeString] = self.connection.encoders[str]
             connection_created.send(sender=self.__class__, connection=self)
-        cursor = CursorWrapper(self.connection.cursor())
-        return cursor
+        cursor = self.connection.cursor()
+        if new_connection:
+            # SQL_AUTO_IS_NULL in MySQL controls whether an AUTO_INCREMENT column
+            # on a recently-inserted row will return when the field is tested for
+            # NULL.  Disabling this value brings this aspect of MySQL in line with
+            # SQL standards.
+            cursor.execute('SET SQL_AUTO_IS_NULL = 0')
+        return CursorWrapper(cursor)
 
     def _rollback(self):
         try:

tests/regressiontests/queries/tests.py

@@ -1070,10 +1070,6 @@ class Queries4Tests(BaseQuerysetTest):
         ci3 = CategoryItem.objects.create(category=c3)
 
         qs = CategoryItem.objects.exclude(category__specialcategory__isnull=False)
-        # Under MySQL, this query gives incorrect values on the first attempt.
-        # If you run exactly the same query twice, it yields the right answer
-        # the second attempt. Oh, how we do love MySQL.
-        qs.count()
         self.assertEqual(qs.count(), 1)
         self.assertQuerysetEqual(qs, [ci1.pk], lambda x: x.pk)
 
@@ -1136,10 +1132,6 @@ class Queries4Tests(BaseQuerysetTest):
         ci3 = CategoryItem.objects.create(category=c1)
 
         qs = CategoryItem.objects.exclude(category__onetoonecategory__isnull=False)
-        # Under MySQL, this query gives incorrect values on the first attempt.
-        # If you run exactly the same query twice, it yields the right answer
-        # the second attempt. Oh, how we do love MySQL.
-        qs.count()
         self.assertEqual(qs.count(), 1)
         self.assertQuerysetEqual(qs, [ci1.pk], lambda x: x.pk)
 
@@ -1421,11 +1413,6 @@ class Queries6Tests(TestCase):
             []
         )
 
-        # This next makes exactly *zero* sense, but it works. It's needed
-        # because MySQL fails to give the right results the first time this
-        # query is executed. If you run the same query a second time, it
-        # works fine. It's a hack, but it works...
-        list(Tag.objects.exclude(children=None))
         self.assertQuerysetEqual(
             Tag.objects.exclude(children=None),
             ['<Tag: t1>', '<Tag: t3>']