56 lines
1.8 KiB
Python
56 lines
1.8 KiB
Python
# Copyright (c) 2015 Mirantis, Inc.
|
|
# All Rights Reserved.
|
|
#
|
|
# Licensed under the Apache License, Version 2.0 (the "License"); you may
|
|
# not use this file except in compliance with the License. You may obtain
|
|
# a copy of the License at
|
|
#
|
|
# http://www.apache.org/licenses/LICENSE-2.0
|
|
#
|
|
# Unless required by applicable law or agreed to in writing, software
|
|
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
|
|
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
|
|
# License for the specific language governing permissions and limitations
|
|
# under the License.
|
|
|
|
"""Utilities for database."""
|
|
from oslo_config import cfg
|
|
from oslo_log import log
|
|
|
|
CONF = cfg.CONF
|
|
LOG = log.getLogger(__name__)
|
|
|
|
|
|
class PluggableBackend(object):
|
|
"""A pluggable backend loaded lazily based on some value."""
|
|
|
|
def __init__(self, pivot, **backends):
|
|
"""Init."""
|
|
self.__backends = backends
|
|
self.__pivot = pivot
|
|
self.__backend = None
|
|
|
|
def __get_backend(self):
|
|
"""Get backend."""
|
|
if not self.__backend:
|
|
backend_name = CONF[self.__pivot]
|
|
if backend_name not in self.__backends: # pragma: no cover
|
|
raise Exception('Invalid backend: %s' % backend_name)
|
|
|
|
backend = self.__backends[backend_name]
|
|
if isinstance(backend, tuple): # pragma: no cover
|
|
name = backend[0]
|
|
fromlist = backend[1]
|
|
else:
|
|
name = backend
|
|
fromlist = backend
|
|
|
|
self.__backend = __import__(name, None, None, fromlist)
|
|
LOG.debug('backend %s', self.__backend)
|
|
return self.__backend
|
|
|
|
def __getattr__(self, key):
|
|
"""Proxy interface to backend."""
|
|
backend = self.__get_backend()
|
|
return getattr(backend, key)
|