Fixed #1142 -- Added multiple database support.

This monster of a patch is the result of Alex Gaynor's 2009 Google Summer of Code project.
Congratulations to Alex for a job well done.

Big thanks also go to:
 * Justin Bronn for keeping GIS in line with the changes,
 * Karen Tracey and Jani Tiainen for their help testing Oracle support
 * Brett Hoerner, Jon Loyens, and Craig Kimmerer for their feedback.
 * Malcolm Treddinick for his guidance during the GSoC submission process.
 * Simon Willison for driving the original design process
 * Cal Henderson for complaining about ponies he wanted.

... and everyone else too numerous to mention that helped to bring this feature into fruition.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11952 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 82 insertions, 0 deletions

diff --git a/django/db/utils.py b/django/db/utils.py
new file mode 100644
index 0000000000..8c0b677156
--- /dev/null
+++ b/django/db/utils.py
@@ -0,0 +1,82 @@
+import inspect
+import os
+
+from django.conf import settings
+from django.core.exceptions import ImproperlyConfigured
+from django.utils.importlib import import_module
+
+def load_backend(backend_name):
+    try:
+        module = import_module('.base', 'django.db.backends.%s' % backend_name)
+        import warnings
+        warnings.warn(
+            "Short names for DATABASE_ENGINE are deprecated; prepend with 'django.db.backends.'",
+            PendingDeprecationWarning
+        )
+        return module
+    except ImportError, e:
+        # Look for a fully qualified database backend name
+        try:
+            return import_module('.base', backend_name)
+        except ImportError, e_user:
+            # The database backend wasn't found. Display a helpful error message
+            # listing all possible (built-in) database backends.
+            backend_dir = os.path.join(os.path.dirname(__file__), 'backends')
+            try:
+                available_backends = [f for f in os.listdir(backend_dir)
+                        if os.path.isdir(os.path.join(backend_dir, f))
+                        and not f.startswith('.')]
+            except EnvironmentError:
+                available_backends = []
+            available_backends.sort()
+            if backend_name not in available_backends:
+                error_msg = ("%r isn't an available database backend. \n" +
+                    "Try using django.db.backends.XXX, where XXX is one of:\n    %s\n" +
+                    "Error was: %s") % \
+                    (backend_name, ", ".join(map(repr, available_backends)), e_user)
+                raise ImproperlyConfigured(error_msg)
+            else:
+                raise # If there's some other error, this must be an error in Django itself.
+
+class ConnectionDoesNotExist(Exception):
+    pass
+
+class ConnectionHandler(object):
+    def __init__(self, databases):
+        self.databases = databases
+        self._connections = {}
+
+    def ensure_defaults(self, alias):
+        """
+        Puts the defaults into the settings dictionary for a given connection
+        where no settings is provided.
+        """
+        try:
+            conn = self.databases[alias]
+        except KeyError:
+            raise ConnectionDoesNotExist("The connection %s doesn't exist" % alias)
+        conn.setdefault('ENGINE', 'dummy')
+        conn.setdefault('OPTIONS', {})
+        conn.setdefault('TEST_CHARSET', None)
+        conn.setdefault('TEST_COLLATION', None)
+        conn.setdefault('TEST_NAME', None)
+        conn.setdefault('TIME_ZONE', settings.TIME_ZONE)
+        for setting in ('NAME', 'USER', 'PASSWORD', 'HOST', 'PORT'):
+            conn.setdefault(setting, '')
+
+    def __getitem__(self, alias):
+        if alias in self._connections:
+            return self._connections[alias]
+
+        self.ensure_defaults(alias)
+        db = self.databases[alias]
+        backend = load_backend(db['ENGINE'])
+        conn = backend.DatabaseWrapper(db, alias)
+        self._connections[alias] = conn
+        return conn
+
+    def __iter__(self):
+        return iter(self.databases)
+
+    def all(self):
+        return [self[alias] for alias in self]