From 72d6cf7fc4a070dbf000fd722b59e54f09a833d3 Mon Sep 17 00:00:00 2001
From: Julien Danjou <julien@danjou.info>
Date: Tue, 30 Sep 2014 17:01:04 +0200
Subject: [PATCH] Replace custom lazy loading by stevedore

Change-Id: I0b09e8822af6e8c3ce7299d31eb53f30a50262bc
---
 ironic/common/utils.py | 35 -----------------------------------
 ironic/db/migration.py | 29 ++++++++++++++++++-----------
 setup.cfg              |  3 +++
 3 files changed, 21 insertions(+), 46 deletions(-)

diff --git a/ironic/common/utils.py b/ironic/common/utils.py
index bd07a8c004..4c6443f65b 100644
--- a/ironic/common/utils.py
+++ b/ironic/common/utils.py
@@ -145,41 +145,6 @@ def random_alnum(size=32):
     return ''.join(random.choice(characters) for _ in range(size))
 
 
-class LazyPluggable(object):
-    """A pluggable backend loaded lazily based on some value."""
-
-    def __init__(self, pivot, config_group=None, **backends):
-        self.__backends = backends
-        self.__pivot = pivot
-        self.__backend = None
-        self.__config_group = config_group
-
-    def __get_backend(self):
-        if not self.__backend:
-            if self.__config_group is None:
-                backend_name = CONF[self.__pivot]
-            else:
-                backend_name = CONF[self.__config_group][self.__pivot]
-            if backend_name not in self.__backends:
-                msg = _('Invalid backend: %s') % backend_name
-                raise exception.IronicException(msg)
-
-            backend = self.__backends[backend_name]
-            if isinstance(backend, tuple):
-                name = backend[0]
-                fromlist = backend[1]
-            else:
-                name = backend
-                fromlist = backend
-
-            self.__backend = __import__(name, None, None, fromlist)
-        return self.__backend
-
-    def __getattr__(self, key):
-        backend = self.__get_backend()
-        return getattr(backend, key)
-
-
 def delete_if_exists(pathname):
     """delete a file, but ignore file not found error."""
 
diff --git a/ironic/db/migration.py b/ironic/db/migration.py
index d5c0fcf10d..cef46860bb 100644
--- a/ironic/db/migration.py
+++ b/ironic/db/migration.py
@@ -16,34 +16,41 @@
 
 """Database setup and migration commands."""
 
-from ironic.common import utils
+from oslo.config import cfg
+from stevedore import driver
 
-IMPL = utils.LazyPluggable(
-    pivot='backend',
-    config_group='database',
-    sqlalchemy='ironic.db.sqlalchemy.migration')
+_IMPL = None
+
+
+def get_backend():
+    global _IMPL
+    if not _IMPL:
+        cfg.CONF.import_opt('backend', 'oslo.db.options', group='database')
+        _IMPL = driver.DriverManager("ironic.database.migration_backend",
+                                     cfg.CONF.database.backend).driver
+    return _IMPL
 
 
 def upgrade(version=None):
     """Migrate the database to `version` or the most recent version."""
-    return IMPL.upgrade(version)
+    return get_backend().upgrade(version)
 
 
 def downgrade(version=None):
-    return IMPL.downgrade(version)
+    return get_backend().downgrade(version)
 
 
 def version():
-    return IMPL.version()
+    return get_backend().version()
 
 
 def stamp(version):
-    return IMPL.stamp(version)
+    return get_backend().stamp(version)
 
 
 def revision(message, autogenerate):
-    return IMPL.revision(message, autogenerate)
+    return get_backend().revision(message, autogenerate)
 
 
 def create_schema():
-    return IMPL.create_schema()
+    return get_backend().create_schema()
diff --git a/setup.cfg b/setup.cfg
index dcb3a33c92..5133398c44 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -60,6 +60,9 @@ ironic.drivers =
     pxe_drac = ironic.drivers.drac:PXEDracDriver
     pxe_snmp = ironic.drivers.pxe:PXEAndSNMPDriver
 
+ironic.database.migration_backend =
+    sqlalchemy = ironic.db.sqlalchemy.migration
+
 [pbr]
 autodoc_index_modules = True