Merge lp:~jkakar/storm/block-access-context-manager into lp:storm

[Jamu Kakar]

This branch introduces the following changes:

- A new block_access context manager blocks database access for one
  or more stores in the managed scope.

[Stuart Bishop (stub)]

The years in the copyright statement in tests/store/block.py are old. Otherwise all good.

review: Approve

[James Henstridge (jamesh)]

It looks like this test will only pass on Python >= 2.6 (since it uses the with statement without a __future__ pragma). Is that desirable?

I don't think there is as much need to keep Python 2.4 compatibility as there once was (Zope 3 and Launchpad have been updated since then), but are we at a point where we want to drop 2.5 support too?

[Jamu Kakar (jkakar)]

James:

Yeah, I wondered about that when I implemented the change. I put it
in its own module to keep Storm workable with older versions of
Python. Perhaps we can do two things to make it better:

1. Use a __future__ import to make it usable with Python 2.5.

2. Add a version check in the tests to make sure the test suite
   continues to run on Python 2.4.

What do you think?

[James Henstridge (jamesh)]

Adding the __future__ import seems worth doing.

I'm not sure whether 2.4 compatibility is that important now though. We mainly kept it for support for apps stuck using versions of Zope 3 from before that framework was updated to work with current versions of Python (namely Launchpad). Given that Zope 3 has moved on, it isn't clear whether we need to maintain 2.4 compatibility now.

In contrast, the previous Ubuntu LTS release (Hardy) didn't have 2.6, so it is quite possible that we've still got some boxes that still don't have 2.6 rolled out yet. I assume it'd be similar for some users on other enterprise distros.

It would be nice to require 2.6 at some point though, since it would let us start preparing for Python 3 support, but I'm not convinced we're there yet.

Anyway: with a __future__ import, I've got no objection to this change.

review: Approve

[Jamu Kakar (jkakar)]

James:

Awesome, thanks, I'll add the __future__ import before merging.
Regarding Python 2.4 my feeling is that we should announce
deprecation when we release 0.18 and then officially drop support
when we release 0.19. That'll give people some heads up about the
change.

[Colin Watson (cjwatson)]

I'm writing this from the increasingly strange future of 2020, where it's very clear we don't need to preserve 2.4 compatibility any more, so I'm going to go ahead and merge this without that (and with just a minor adjustment to cope with tests.* having been moved to storm.tests.*).

review: Approve

=== modified file 'storm/store.py'
--- storm/store.py	2010-08-05 19:43:41 +0000
+++ storm/store.py	2010-08-13 02:57:43 +0000
@@ -1805,3 +1805,21 @@
     pass
 
 AutoReload = AutoReload()
+
+
+class block_access(object):
+    """
+    Context manager blocks database access by one or more L{Store}s in the
+    managed scope.
+    """
+
+    def __init__(self, *args):
+        self.stores = args
+
+    def __enter__(self):
+        for store in self.stores:
+            store.block_access()
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        for store in self.stores:
+            store.unblock_access()
 
=== added file 'tests/store/block.py'
--- tests/store/block.py	1970-01-01 00:00:00 +0000
+++ tests/store/block.py	2010-08-13 02:57:43 +0000
@@ -0,0 +1,61 @@
+# Copyright (c) 2006, 2007 Canonical
+#
+# Written by Gustavo Niemeyer <[e-mail]>
+#
+# This file is part of Storm Object Relational Mapper.
+#
+# Storm is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as
+# published by the Free Software Foundation; either version 2.1 of
+# the License, or (at your option) any later version.
+#
+# Storm is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from storm.databases.sqlite import SQLite
+from storm.exceptions import ConnectionBlockedError
+from storm.store import Store, block_access
+from storm.uri import URI
+
+from tests.helper import TestHelper, MakePath
+
+
+class BlockAccessTest(TestHelper):
+    """Tests for L{block_access}."""
+
+    helpers = [MakePath]
+
+    def setUp(self):
+        super(BlockAccessTest, self).setUp()
+        database = SQLite(URI("sqlite:"))
+        self.store = Store(database)
+
+    def test_block_access(self):
+        """
+        The L{block_access} context manager blocks access to a L{Store}.  A
+        L{ConnectionBlockedError} exception is raised if an attempt to access
+        the underlying database is made while a store is blocked.
+        """
+        with block_access(self.store):
+            self.assertRaises(ConnectionBlockedError, self.store.execute,
+                              "SELECT 1")
+        result = self.store.execute("SELECT 1")
+        self.assertEqual([(1,)], list(result))
+
+    def test_block_access_with_multiple_stores(self):
+        """
+        If multiple L{Store}s are passed to L{block_access} they will all be
+        blocked until the managed context is left.
+        """
+        database = SQLite(URI("sqlite:%s" % self.make_path()))
+        store = Store(database)
+        with block_access(self.store, store):
+            self.assertRaises(ConnectionBlockedError, self.store.execute,
+                              "SELECT 1")
+            self.assertRaises(ConnectionBlockedError, store.execute,
+                              "SELECT 1")