Add setuptools plug-in entry point for defining different database backends.

Now someone could distribute a setuptools package that provided say, a MySQL
database implementation and very easily override the stock database.  How
awesome is setuptools?

Removed MANAGERS_INIT_FUNCTION since setuptools gives us a much more standard
way of defining this plug-in entry point.  Remove other old crud from
Defaults.py.

Restructure our own 'stock' database backend to be a plugin so it's totally on
par with any other package.  The only special case is that if more than one
such entry point is defined, we filter out the 'stock' one (i.e. ours) under
the assumption that the user is overriding it.  If we still have more than one
plug-in, it's an error.

Restructure the initialization subsystem to use the plug-in, doing all the
proper assertions and what not.  The IDatabase interface defines what the
database back-end plugin must provide.  I've no doubt this will eventually
need a bit more fleshing out, but it gives all this stuff a principled hook
point instead of something ad-hoc.

1 files changed, 31 insertions, 16 deletions

diff --git a/Mailman/database/__init__.py b/Mailman/database/__init__.py
index 6c6312d0a..d50c33973 100644
--- a/Mailman/database/__init__.py
+++ b/Mailman/database/__init__.py
@@ -20,30 +20,45 @@ from __future__ import with_statement
 import os
 
 from elixir import objectstore
+from zope.interface import implements
 
+from Mailman.interfaces import IDatabase
 from Mailman.database.listmanager import ListManager
 from Mailman.database.usermanager import UserManager
 
+__metaclass__ = type
 __all__ = [
-    'initialize',
-    'flush',
+    'StockDatabase',
+    'flush', # for test convenience
     ]
 
+flush = None
+
 
 
-def initialize():
-    from Mailman.LockFile import LockFile
-    from Mailman.configuration import config
-    from Mailman.database import model
-    # Serialize this so we don't get multiple processes trying to create the
-    # database at the same time.
-    lockfile = os.path.join(config.LOCK_DIR, '<dbcreatelock>')
-    with LockFile(lockfile):
-        model.initialize()
-    config.list_manager = ListManager()
-    config.user_manager = UserManager()
-    flush()
+class StockDatabase:
+    implements(IDatabase)
+
+    def __init__(self):
+        # Expose the flush() method for test case convenience using the stock
+        # database.
+        global flush
+        flush = self.flush
+        self.list_manager = None
+        self.user_manager = None
 
+    def initialize(self):
+        from Mailman.LockFile import LockFile
+        from Mailman.configuration import config
+        from Mailman.database import model
+        # Serialize this so we don't get multiple processes trying to create the
+        # database at the same time.
+        lockfile = os.path.join(config.LOCK_DIR, '<dbcreatelock>')
+        with LockFile(lockfile):
+            model.initialize()
+        self.list_manager = ListManager()
+        self.user_manager = UserManager()
+        self.flush()
 
-def flush():
-    objectstore.flush()
+    def flush(self):
+        objectstore.flush()