Add a 'connection-class' key to the database definition which you may use to...

Add a 'connection-class' key to the database definition which you may use to override the stock ZODB Connection class for a given database via the config file.

lib/python/Zope/Startup/datatypes.py

@@ -15,6 +15,8 @@
 """Datatypes for the Zope schema for use with ZConfig."""
 
 import os
+from ZODB.config import ZODBDatabase
+from ZODB.config import FileStorage
 
 # generic datatypes
 
@@ -78,6 +80,27 @@ def mount_point(value):
                            "begin with a slash" % value)
     return value
 
+# A datatype that converts a Python dotted-path-name to an object
+
+def importable_name(name):
+    try:
+        components = name.split('.')
+        start = components[0]
+        g = globals()
+        package = __import__(start, g, g)
+        modulenames = [start]
+        for component in components[1:]:
+            modulenames.append(component)
+            try:
+                package = getattr(package, component)
+            except AttributeError:
+                n = '.'.join(modulenames)
+                package = __import__(n, g, g, component)
+        return package
+    except ImportError:
+        raise ValueError, (
+            'The object named by "%s" could not be imported' %  name )
+
 # Datatype for the root configuration object
 # (adds the softwarehome and zopehome fields; default values for some
 #  computed paths)
@@ -119,17 +142,25 @@ def root_config(section):
 
     return section
 
+class ZopeDatabase(ZODBDatabase):
+    """ A ZODB database datatype that can handle an extended set of
+    attributes """
+    def open(self):
+        DB = ZODBDatabase.open(self)
+        # set the connection class
+        DB.klass = self.config.connection_class
+        return DB
+    
 def getDefaultDatabaseFactory(context):
     # default to a filestorage named 'Data.fs' in clienthome
-    from ZODB.config import FileStorage
-    from ZODB.config import ZODBDatabase
-
     class dummy:
         def __init__(self, name):
             self.name = name
         def getSectionName(self):
             return self.name
 
+    from ZODB.Connection import Connection
+
     path = os.path.join(context.clienthome, 'Data.fs')
     fs_ns = dummy('default filestorage at %s' % path)
     fs_ns.path = path
@@ -144,4 +175,6 @@ def getDefaultDatabaseFactory(context):
     db_ns.version_pool_size=3
     db_ns.version_cache_size = 100
     db_ns.mount_points = ['/']
-    return ZODBDatabase(db_ns)
+    db_ns.connection_class = Connection
+    return ZopeDatabase(db_ns)
+

lib/python/Zope/Startup/tests/test_schema.py

@@ -95,6 +95,23 @@ class StartupTestCase(unittest.TestCase):
             """)
         self.assert_(isinstance(conf.dns_resolver, resolver.caching_resolver))
 
+    def test_zodb_db(self):
+        conf = self.load_config_text("""\
+            instancehome <<INSTANCE_HOME>>
+            <zodb_db main>
+              <filestorage>
+               path <<INSTANCE_HOME>>/var/Data.fs
+               </filestorage>
+                connection-class  Products.TemporaryFolder.LowConflictConnection.LowConflictConnection
+                mount-point                    /
+                cache-size                     5000
+                pool-size                      7
+                version-pool-size              3
+                version-cache-size             100
+            </zodb_db>
+            """)
+        self.assertEqual(conf.databases[0].config.connection_class.__name__,
+                         'LowConflictConnection')
 
 def test_suite():
     return unittest.makeSuite(StartupTestCase)

lib/python/Zope/Startup/zopeschema.xml

@@ -121,8 +121,9 @@
 
   </sectiontype>
 
-  <sectiontype name="zodb_db" datatype="ZODB.config.ZODBDatabase"
+  <sectiontype name="zodb_db" datatype=".ZopeDatabase"
                implements="ZODB.database" extends="zodb">
+
     <description>
       We need to specialize the database configuration section for Zope
       only by including a (required) mount-point argument, which
@@ -131,6 +132,15 @@
     </description>
     <multikey name="mount-point" required="yes" attribute="mount_points"
               datatype=".mount_point"/>
+
+    <description>
+     We want to allow people to be able to change the connection
+     class a database uses on a per-database basis to support
+     different connection policies.
+    </description>
+    <key name="connection-class" datatype=".importable_name"
+              default="ZODB.Connection.Connection"/>
+
   </sectiontype>
 
   <!-- end of type definitions -->
@@ -273,7 +283,7 @@
     </description>
   </key>
 
-  <multisection type="ZODB.database" name="+" attribute="databases">
+  <multisection type="zodb_db" name="+" attribute="databases">
     <description>
        Zope ZODB databases must have a name, and they are required to be
        referenced via the "zodb_db" database type because it is