Fix usage of oslo.config

- make it possible to create a DBAPI instance given a config instance

- remove usage of global cfg.CONF instance (it's up to a user to pass
  a ConfigOpts instance to oslo.db)

- ensure end applications don't need to import/register/use config
  options directly - instead they pass a config instance to oslo.db
  helpers (EngineFacade.from_config() and DBAPI.from_config() class
  methods)

At the same time, usage of oslo.config remains completely optional as
we provide an API to pass those parameters programatically.

Change-Id: I1a00db7a4200ebdc96f17256ecbad430477e868f

1 files changed, 3 insertions, 5 deletions

diff --git a/doc/source/usage.rst b/doc/source/usage.rst
index be9ff69..0e5a2f2 100644
--- a/doc/source/usage.rst
+++ b/doc/source/usage.rst
@@ -8,6 +8,7 @@ To use oslo.db in a project::
   
   .. code:: python
 
+    from oslo.config import cfg
     from oslo.db.sqlalchemy import session as db_session
 
     _FACADE = None
@@ -15,8 +16,7 @@ To use oslo.db in a project::
     def _create_facade_lazily():
         global _FACADE
         if _FACADE is None:
-            _FACADE = db_session.EngineFacade.from_config(
-                CONF.database.connection, CONF)
+            _FACADE = db_session.EngineFacade.from_config(cfg.CONF)
         return _FACADE
 
     def get_engine():
@@ -48,12 +48,10 @@ To use oslo.db in a project::
     from oslo.config import cfg
     from oslo.db import api as db_api
 
-    CONF = cfg.CONF
-    CONF.import_opt('backend', 'oslo.db.options', group='database')
 
     _BACKEND_MAPPING = {'sqlalchemy': 'project.db.sqlalchemy.api'}
 
-    IMPL = db_api.DBAPI(CONF.database.backend, backend_mapping=_BACKEND_MAPPING)
+    IMPL = db_api.DBAPI.from_config(cfg.CONF, backend_mapping=_BACKEND_MAPPING)
 
     def get_engine():
         return IMPL.get_engine()