# HG changeset patch
# User paulb
# Date 1196469209 0
# Node ID 94d0e64c5c66552f6bc893f2ba314a233b646093
# Parent  05f30cae9f0e82853b09d436d03234c0dbc0282c
[project @ 2007-12-01 00:33:29 by paulb]
Added a StoreSelector for database-related applications.

diff -r 05f30cae9f0e -r 94d0e64c5c66 WebStack/Resources/Selectors.py
--- a/WebStack/Resources/Selectors.py	Sat Dec 01 00:33:16 2007 +0000
+++ b/WebStack/Resources/Selectors.py	Sat Dec 01 00:33:29 2007 +0000
@@ -99,4 +99,41 @@
         trans.default_charset = self.encoding
         self.resource.respond(trans)
 
+class StoreSelector:
+
+    """
+    Maintain an attribute for a data store on transactions, performing an
+    automatic rollback after the transaction has finished. The data store can be
+    a DB-API connection object or any object providing a 'rollback' method.
+    """
+
+    def __init__(self, resource, store):
+
+        """
+        Initialise the selector with a 'resource' (to which all requests shall
+        be forwarded), providing a 'store' which shall be maintained as an
+        attribute.
+        """
+
+        self.resource = resource
+        self.store = store
+
+    def respond(self, trans):
+
+        """
+        Respond to the transaction 'trans' by setting the "store" attribute to
+        refer to the 'store' attribute on this object, then forwarding the
+        transaction to the previously specified resource.
+
+        Regardless of how the resource completes its processing, the 'rollback'
+        method of the store will then be called in order to terminate any
+        unfinished, uncommitted transactions.
+        """
+
+        trans.get_attributes()["store"] = self.store
+        try:
+            self.resource.respond(trans)
+        finally:
+            self.store.rollback()
+
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