From 8217b91aa47063aca0ae0e55cf85cace0ea1ba3f Mon Sep 17 00:00:00 2001
From: Lance Edgar <lance@edbob.org>
Date: Wed, 14 Nov 2012 05:06:31 -0800
Subject: [PATCH] add sqlerror_tween

---
 edbob/pyramid/tweens.py                       | 59 +++++++++++++++++++
 .../edbob/+package+/pyramid/__init__.py_tmpl  | 26 ++++----
 2 files changed, 70 insertions(+), 15 deletions(-)
 create mode 100644 edbob/pyramid/tweens.py

diff --git a/edbob/pyramid/tweens.py b/edbob/pyramid/tweens.py
new file mode 100644
index 0000000..8039efa
--- /dev/null
+++ b/edbob/pyramid/tweens.py
@@ -0,0 +1,59 @@
+#!/usr/bin/env python
+# -*- coding: utf-8  -*-
+################################################################################
+#
+#  edbob -- Pythonic Software Framework
+#  Copyright © 2010-2012 Lance Edgar
+#
+#  This file is part of edbob.
+#
+#  edbob is free software: you can redistribute it and/or modify it under the
+#  terms of the GNU Affero General Public License as published by the Free
+#  Software Foundation, either version 3 of the License, or (at your option)
+#  any later version.
+#
+#  edbob 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 Affero General Public License for
+#  more details.
+#
+#  You should have received a copy of the GNU Affero General Public License
+#  along with edbob.  If not, see <http://www.gnu.org/licenses/>.
+#
+################################################################################
+
+"""
+``edbob.pyramid.tweens`` -- Tween Factories
+"""
+
+import sqlalchemy.exc
+
+from transaction.interfaces import TransientError
+
+
+def sqlerror_tween_factory(handler, registry):
+    """
+    Produces a tween which will convert ``sqlalchemy.exc.OperationalError``
+    instances (caused by database server restart) into a retryable
+    ``transaction.interfaces.TransientError`` instance, so that a second
+    attempt may be made to connect to the database before really giving up.
+
+    .. note::
+       This tween alone is not enough to cause the transaction to be retried;
+       it only marks the error as being *retryable*.  If you wish more than one
+       attempt to be made, you must define the ``tm.attempts`` setting within
+       your Pyramid app configuration.  See `Retrying
+       <http://docs.pylonsproject.org/projects/pyramid_tm/en/latest/#retrying>`_
+       for more information.
+    """
+
+    def sqlerror_tween(request):
+        try:
+            response = handler(request)
+        except sqlalchemy.exc.OperationalError, error:
+            if error.connection_invalidated:
+                raise TransientError(str(error))
+            raise
+        return response
+
+    return sqlerror_tween
diff --git a/edbob/scaffolds/edbob/+package+/pyramid/__init__.py_tmpl b/edbob/scaffolds/edbob/+package+/pyramid/__init__.py_tmpl
index efdc27d..155371b 100644
--- a/edbob/scaffolds/edbob/+package+/pyramid/__init__.py_tmpl
+++ b/edbob/scaffolds/edbob/+package+/pyramid/__init__.py_tmpl
@@ -7,10 +7,8 @@
 import os.path
 
 from pyramid.config import Configurator
-from pyramid.authentication import SessionAuthenticationPolicy
 
 import edbob
-from edbob.pyramid.auth import EdbobAuthorizationPolicy
 
 
 def main(global_config, **settings):
@@ -27,24 +25,18 @@ def main(global_config, **settings):
     # * Raise an exception if a setting is missing or invalid.
     # * Convert values from strings to their intended type.
 
-    settings['mako.directories'] = [
-        '{{package}}.pyramid:templates',
-        'edbob.pyramid:templates',
-        ]
+    settings.setdefault('mako.directories', [
+            '{{package}}.pyramid:templates',
+            'edbob.pyramid:templates',
+            ])
+    
+    # Make two attempts when "retryable" errors happen during transactions.
+    settings.setdefault('tm.attempts', 2)
     
     config = Configurator(settings=settings)
 
     # Configure edbob
     edbob.init('{{package}}', os.path.abspath(settings['edbob.config']))
-
-    # Configure session
-    config.include('pyramid_beaker')
-
-    # Configure auth
-    config.set_authentication_policy(SessionAuthenticationPolicy())
-    config.set_authorization_policy(EdbobAuthorizationPolicy())
-
-    # Include "core" stuff provided by edbob.
     config.include('edbob.pyramid')
 
     # Additional config is defined elsewhere within {{project}}.  This includes
@@ -53,4 +45,8 @@ def main(global_config, **settings):
     config.include('{{package}}.pyramid.subscribers')
     config.include('{{package}}.pyramid.views')
 
+    # Consider PostgreSQL server restart errors to be "retryable."
+    config.add_tween('edbob.pyramid.tweens.sqlerror_tween_factory',
+                     under='pyramid_tm.tm_tween_factory')
+
     return config.make_wsgi_app()