text: # vim: tabstop=4 shiftwidth=4 softtabstop=4
  
  # Copyright 2012 OpenStack LLC.
  #
  #    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 sqlalchemy import Boolean, Column, DateTime, BigInteger
  from sqlalchemy import MetaData, Integer, String, Table
  
  from nova.openstack.common import log as logging
  
  LOG = logging.getLogger(__name__)
  
  
  def upgrade(migrate_engine):
      meta = MetaData()
      meta.bind = migrate_engine
  
      # add column:
      bw_usage_cache = Table('bw_usage_cache', meta, autoload=True)
      uuid = Column('uuid', String(36))
  
      # clear the cache to get rid of entries with no uuid
      migrate_engine.execute(bw_usage_cache.delete())
  
      bw_usage_cache.create_column(uuid)
  
  
  def downgrade(migrate_engine):
      meta = MetaData()
      meta.bind = migrate_engine
  
      # drop column:
      bw_usage_cache = Table('bw_usage_cache', meta,
          Column('created_at', DateTime(timezone=False)),
          Column('updated_at', DateTime(timezone=False)),
          Column('deleted_at', DateTime(timezone=False)),
          Column('deleted', Boolean(create_constraint=True, name=None)),
          Column('id', Integer(), primary_key=True, nullable=False),
          Column('mac', String(255)),
          Column('uuid', String(36)),
          Column('start_period', DateTime(timezone=False), nullable=False),
          Column('last_refreshed', DateTime(timezone=False)),
          Column('bw_in', BigInteger()),
          Column('bw_out', BigInteger()),
          extend_existing=True)
  
      bw_usage_cache.drop_column('uuid')
  