Ticket #17671: django-ticket17671.diff

django/db/backends/util.py

@@ -30 +30 @@
     def __iter__(self):
         return iter(self.cursor)
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        # Ticket #17671 - Close instead of passing thru to avoid backend 
+        # specific behavior.
+        self.cursor.close()
 
 class CursorDebugWrapper(CursorWrapper):
 

docs/releases/1.5.txt

@@ -144 +144 @@
 hashing methods need byte strings, you can use the
 :func:`~django.utils.encoding.smart_str` utility to encode the strings.
 
+Using database cursors as context managers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Prior to Python 2.6, database cursors could be used as a context manager. The
+specific backend's cursor defined the behavior of the context manager. The
+behavior of magic method lookups was changed with Python 2.7 and cursors were
+no longer usable as context managers. 
+
+Django 1.5 allows a cursor to be used as a context manager that is a shortcut
+for the following, instead of backend specific behavior.
+
+.. code-block:: python
+
+    c = connection.cursor()
+    try:
+        c.execute(...)
+    finally:
+        c.close()
+
 Features deprecated in 1.5
 ==========================
 

docs/topics/db/sql.txt

@@ -262 +262 @@
     [{'parent_id': None, 'id': 54360982L}, {'parent_id': None, 'id': 54360880L}]
 
 
+
 .. _transactions-and-raw-sql:
 
 Transactions and raw SQL
@@ -290 +291 @@
 escaping to your parameter(s) as necessary. (Also note that Django expects the
 ``"%s"`` placeholder, *not* the ``"?"`` placeholder, which is used by the SQLite
 Python bindings. This is for the sake of consistency and sanity.)
+
+.. versionchanged:: 1.5
+
+:pep:`249` does not state whether a cursor should be usable as a context
+manager. Prior to Python 2.7, a cursor was usable as a context manager due
+an unexpected behavior in magic method lookups (`Python ticket #9220`_). 
+Django 1.5 explicitly added support to allow using a cursor as context 
+manager.
+
+.. _`Python ticket #9220`: http://bugs.python.org/issue9220
+
+Using a cursor as a context manager:
+
+.. code-block:: python
+
+    with connection.cursor() as c:
+        c.execute(...)
+
+is equivalent to:
+
+.. code-block:: python
+
+    c = connection.cursor()
+    try:
+        c.execute(...)
+    finally:
+        c.close()

tests/regressiontests/backends/tests.py

@@ -416 +416 @@
         with self.assertRaises(DatabaseError):
             cursor.execute(query)
 
+    def test_cursor_contextmanager(self):
+        """
+        Test that cursors can be used as a context manager
+        """
+        with connection.cursor() as cursor:
+            from django.db.backends.util import CursorWrapper
+            self.assertTrue(isinstance(cursor, CursorWrapper))
+
 # We don't make these tests conditional because that means we would need to
 # check and differentiate between:
 # * MySQL+InnoDB, MySQL+MYISAM (something we currently can't do).