text: # Copyright 2011 OpenStack LLC.
  # 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 sqlalchemy import MetaData, Table
  from migrate import ForeignKeyConstraint
  
  from nova import log as logging
  
  LOG = logging.getLogger(__name__)
  
  
  def upgrade(migrate_engine):
      meta = MetaData()
      meta.bind = migrate_engine
      dialect = migrate_engine.url.get_dialect().name
  
      # grab tables
      fixed_ips = Table('fixed_ips', meta, autoload=True)
      virtual_interfaces = Table('virtual_interfaces', meta, autoload=True)
  
      # add foreignkey if not sqlite
      try:
          if not dialect.startswith('sqlite'):
              ForeignKeyConstraint(columns=[fixed_ips.c.virtual_interface_id],
                                   refcolumns=[virtual_interfaces.c.id]).create()
      except Exception:
          LOG.error(_("foreign key constraint couldn't be added"))
          raise
  
  
  def downgrade(migrate_engine):
      meta = MetaData()
      meta.bind = migrate_engine
      dialect = migrate_engine.url.get_dialect().name
  
      # grab tables
      fixed_ips = Table('fixed_ips', meta, autoload=True)
      virtual_interfaces = Table('virtual_interfaces', meta, autoload=True)
  
      # drop foreignkey if not sqlite
      try:
          if not dialect.startswith('sqlite'):
              ForeignKeyConstraint(columns=[fixed_ips.c.virtual_interface_id],
                                   refcolumns=[virtual_interfaces.c.id]).drop()
      except Exception:
          LOG.error(_("foreign key constraint couldn't be dropped"))
          raise
  