Remove models usage from migrations

Models shouldn't be used in migrations because
they represents only latest state of appropriate
tables.

Closes-Bug: #1473885
Change-Id: Ic8313fda4e82232bb71212c4bd8d882b84770789

manila/db/migrations/alembic/versions/3db9992c30f3_transform_statuses_to_lowercase.py

@@ -28,26 +28,30 @@ down_revision = '533646c7af38'
 from alembic import op
 import sqlalchemy as sa
 
-from manila.db.sqlalchemy import models
+from manila.db.migrations import utils
 
 
 def upgrade():
     # NOTE(vponomaryov): shares has some statuses as uppercase, so
     # transform them in addition to statuses of share servers.
-    for model in (models.Share, models.ShareServer):
-        _transform_case(model, make_upper=False)
+    for table in ('shares', 'share_servers'):
+        _transform_case(table, make_upper=False)
 
 
 def downgrade():
     # NOTE(vponomaryov): transform share server statuses to uppercase and
     # leave share statuses as is.
-    _transform_case(models.ShareServer, make_upper=True)
+    _transform_case('share_servers', make_upper=True)
 
 
-def _transform_case(model, make_upper):
+def _transform_case(table_name, make_upper):
     connection = op.get_bind()
-    session = sa.orm.Session(bind=connection.connect())
+    table = utils.load_table(table_name, connection)
     case = sa.func.upper if make_upper else sa.func.lower
-    session.query(model).update(
-        {model.status: case(model.status)}, synchronize_session='fetch')
-    session.commit()
+
+    for row in connection.execute(table.select()):
+        op.execute(
+            table.update().where(
+                table.c.id == row.id
+            ).values({'status': case(row.status)})
+        )

manila/db/migrations/utils.py

@@ -0,0 +1,21 @@
+# Copyright 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.
+
+import sqlalchemy as sa
+
+
+def load_table(name, connection):
+    return sa.Table(name, sa.MetaData(), autoload=True,
+                    autoload_with=connection)

manila/tests/db/migrations/test_utils.py

@@ -0,0 +1,30 @@
+# Copyright 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.
+
+from manila.db.migrations import utils
+from manila.db.sqlalchemy import api
+from manila import test
+
+
+class MigrationUtilsTestCase(test.TestCase):
+
+    def test_load_table(self):
+        connection = api.get_engine()
+        table_name = 'shares'
+
+        actual_result = utils.load_table(table_name, connection)
+
+        self.assertIsNotNone(actual_result)
+        self.assertEqual(table_name, actual_result.name)