New engine facade from oslo_db: Step 1

Start using new engine facade.
Existing property session for Context is needed for backward
compatibility.
Temporary created class ContextBaseWithSession unless
reader and writer will be used in proper places.
Usage of lazy init for engine facade will be removed in next patch
set.

Partial-Bug: #1520719

Change-Id: I4f0693789f1c928ef47c5fdd982c147d1a9a89e1

neutron/context.py

@@ -19,6 +19,7 @@ import copy
 import datetime
 
 from oslo_context import context as oslo_context
+from oslo_db.sqlalchemy import enginefacade
 
 from neutron.db import api as db_api
 from neutron import policy
@@ -109,13 +110,22 @@ class ContextBase(oslo_context.RequestContext):
         return context
 
 
-class Context(ContextBase):
+@enginefacade.transaction_context_provider
+class ContextBaseWithSession(ContextBase):
+    pass
+
+
+class Context(ContextBaseWithSession):
     def __init__(self, *args, **kwargs):
         super(Context, self).__init__(*args, **kwargs)
         self._session = None
 
     @property
     def session(self):
+        # TODO(akamyshnikova): checking for session attribute won't be needed
+        # when reader and writer will be used
+        if hasattr(super(Context, self), 'session'):
+            return super(Context, self).session
         if self._session is None:
             self._session = db_api.get_session()
         return self._session

neutron/db/api.py

@@ -20,12 +20,14 @@ from neutron_lib import exceptions as n_exc
 from oslo_config import cfg
 from oslo_db import api as oslo_db_api
 from oslo_db import exception as db_exc
-from oslo_db.sqlalchemy import session
+from oslo_db.sqlalchemy import enginefacade
 from oslo_utils import excutils
 from oslo_utils import uuidutils
 
 from neutron.db import common_db_mixin
 
+context_manager = enginefacade.transaction_context()
+
 
 _FACADE = None
 
@@ -53,7 +55,8 @@ def _create_facade_lazily():
     global _FACADE
 
     if _FACADE is None:
-        _FACADE = session.EngineFacade.from_config(cfg.CONF, sqlite_fk=True)
+        context_manager.configure(sqlite_fk=True, **cfg.CONF.database)
+        _FACADE = context_manager._factory.get_legacy_facade()
 
     return _FACADE
 

neutron/tests/unit/services/metering/test_metering_plugin.py

@@ -18,6 +18,7 @@ from oslo_utils import uuidutils
 from neutron.api.v2 import attributes as attr
 from neutron import context
 from neutron.db import agents_db
+from neutron.db import api as db_api
 from neutron.db import l3_agentschedulers_db
 from neutron.db.metering import metering_rpc
 from neutron.extensions import l3 as ext_l3
@@ -57,6 +58,20 @@ class MeteringTestExtensionManager(object):
         return []
 
 
+# TODO(akamyshnikova):we need this temporary FakeContext class while Context
+# checking for existence of session attribute.
+class FakeContext(context.ContextBaseWithSession):
+    def __init__(self, *args, **kwargs):
+        super(FakeContext, self).__init__(*args, **kwargs)
+        self._session = None
+
+    @property
+    def session(self):
+        if self._session is None:
+            self._session = db_api.get_session()
+        return self._session
+
+
 class TestMeteringPlugin(test_db_base_plugin_v2.NeutronDbPluginV2TestCase,
                          test_l3.L3NatTestCaseMixin,
                          test_metering_db.MeteringPluginDbTestCaseMixin):
@@ -81,7 +96,7 @@ class TestMeteringPlugin(test_db_base_plugin_v2.NeutronDbPluginV2TestCase,
         self.mock_uuid = self.uuid_patch.start()
 
         self.tenant_id = 'a7e61382-47b8-4d40-bae3-f95981b5637b'
-        self.ctx = context.Context('', self.tenant_id, is_admin=True)
+        self.ctx = FakeContext('', self.tenant_id, is_admin=True)
         self.context_patch = mock.patch('neutron.context.Context',
                                         return_value=self.ctx)
         self.mock_context = self.context_patch.start()
@@ -309,7 +324,7 @@ class TestMeteringPluginL3AgentScheduler(
         self.mock_uuid = self.uuid_patch.start()
 
         self.tenant_id = 'a7e61382-47b8-4d40-bae3-f95981b5637b'
-        self.ctx = context.Context('', self.tenant_id, is_admin=True)
+        self.ctx = FakeContext('', self.tenant_id, is_admin=True)
         self.context_patch = mock.patch('neutron.context.Context',
                                         return_value=self.ctx)
         self.mock_context = self.context_patch.start()