[placement] add a placement_aggregates table to api_db

In order to facilitate a future extraction of the placement service
we want to record the association between a resource provider and an
arbitrary aggregate uuid in its own table.

A PlacementAggregate model is joined from ResourceProvider via
ResourceProviderAggregate. Note that this structure is used so we can
join on ids instead of strings (the uuids). A direct mapping between
ResourceProvider uuid and Aggregate uuid was mooted earlier in the year
but was determined to be suboptimal.

The name 'placement_aggregates' is used as the least problematic of
several choices after discussion amongst several parties.

The data will be used by the forthcoming get_ and set_aggregates
methods on the ResourceProvider object.

Change-Id: Id0355cb022f68e962af306ff04cf724d22b68d19
Partially-Implements: blueprint generic-resource-pools-ocata

nova/db/sqlalchemy/api_migrations/migrate_repo/versions/029_placement_aggregates.py

@@ -0,0 +1,37 @@
+#    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.
+"""API Database migrations for placement_aggregates"""
+
+from migrate import UniqueConstraint
+from sqlalchemy import Column
+from sqlalchemy import DateTime
+from sqlalchemy import Integer
+from sqlalchemy import MetaData
+from sqlalchemy import String
+from sqlalchemy import Table
+
+
+def upgrade(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+
+    placement_aggregates = Table('placement_aggregates', meta,
+        Column('created_at', DateTime),
+        Column('updated_at', DateTime),
+        Column('id', Integer, primary_key=True, nullable=False),
+        Column('uuid', String(length=36), index=True),
+        UniqueConstraint('uuid', name='uniq_placement_aggregates0uuid'),
+        mysql_engine='InnoDB',
+        mysql_charset='latin1'
+    )
+
+    placement_aggregates.create(checkfirst=True)

nova/db/sqlalchemy/api_models.py

@@ -371,6 +371,17 @@ class ResourceProviderAggregate(API_BASE):
     aggregate_id = Column(Integer, primary_key=True, nullable=False)
 
 
+class PlacementAggregate(API_BASE):
+    """A grouping of resource providers."""
+    __tablename__ = 'placement_aggregates'
+    __table_args__ = (
+        schema.UniqueConstraint("uuid", name="uniq_placement_aggregates0uuid"),
+    )
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    uuid = Column(String(36), index=True)
+
+
 class InstanceGroupMember(API_BASE):
     """Represents the members for an instance group."""
     __tablename__ = 'instance_group_member'

nova/tests/functional/db/api/test_migrations.py

@@ -571,6 +571,10 @@ class NovaAPIMigrationsWalk(test_migrations.WalkVersionsMixin):
         self.assertEqual('{"uuid": "foo", "name": "bar"}',
                          fake_build_req.instance)
 
+    def _check_029(self, engine, data):
+        for column in ['created_at', 'updated_at', 'id', 'uuid']:
+            self.assertColumnExists(engine, 'placement_aggregates', column)
+
 
 class TestNovaAPIMigrationsWalkSQLite(NovaAPIMigrationsWalk,
                                       test_base.DbTestCase,