old_contents: # vim: tabstop=4 shiftwidth=4 softtabstop=4
  
  # 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.
  
  import sqlalchemy
  from sqlalchemy import select, Column, ForeignKey, Integer, String
  from migrate import ForeignKeyConstraint
  
  from nova import log as logging
  
  
  LOG = logging.getLogger('nova.db.sqlalchemy.migrate_repo.versions')
  meta = sqlalchemy.MetaData()
  
  
  def _get_table(name):
      return sqlalchemy.Table(name, meta, autoload=True)
  
  
  def upgrade(migrate_engine):
      meta.bind = migrate_engine
      dialect = migrate_engine.url.get_dialect().name
      instance_actions = _get_table('instance_actions')
      instances = _get_table('instances')
      uuid_column = Column('instance_uuid', String(36),
                           ForeignKey('instances.uuid'))
      uuid_column = Column('instance_uuid', String(36))
      uuid_column.create(instance_actions)
  
      try:
          instance_actions.update().values(
              instance_uuid=select(
                  [instances.c.uuid],
                  instances.c.id == instance_actions.c.instance_id)
          ).execute()
      except Exception:
          uuid_column.drop()
          raise
  
      if not dialect.startswith('sqlite'):
          try:
              fkey_name = list(instance_actions.c.instance_id.foreign_keys)[0].\
                               constraint.name
              ForeignKeyConstraint(columns=[instance_actions.c.instance_id],
                                   refcolumns=[instances.c.id],
                                   name=fkey_name).drop()
          except Exception:
              logging.error(_("foreign key constraint couldn't be removed"))
              raise
  
      instance_actions.c.instance_id.drop()
  
  
  def downgrade(migrate_engine):
      meta.bind = migrate_engine
      instance_actions = _get_table('instance_actions')
      instances = _get_table('instances')
      id_column = Column('instance_id', Integer, ForeignKey('instances.id'))
      id_column.create(instance_actions)
  
      try:
          instance_actions.update().values(
              instance_id=select(
                  [instances.c.id],
                  instances.c.uuid == instance_actions.c.instance_uuid)
          ).execute()
      except Exception:
          id_column.drop()
          raise
  
      instance_actions.c.instance_uuid.drop()
  
new_contents: # vim: tabstop=4 shiftwidth=4 softtabstop=4
  
  # 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.
  
  import sqlalchemy
  from sqlalchemy import select, Column, ForeignKey, Integer, String
  from migrate import ForeignKeyConstraint
  
  from nova import log as logging
  
  
  LOG = logging.getLogger('nova.db.sqlalchemy.migrate_repo.versions')
  meta = sqlalchemy.MetaData()
  
  
  def _get_table(name):
      return sqlalchemy.Table(name, meta, autoload=True)
  
  
  def upgrade(migrate_engine):
      meta.bind = migrate_engine
      instance_actions = _get_table('instance_actions')
      instances = _get_table('instances')
      uuid_column = Column('instance_uuid', String(36),
                           ForeignKey('instances.uuid'))
      uuid_column = Column('instance_uuid', String(36))
      uuid_column.create(instance_actions)
  
      try:
          instance_actions.update().values(
              instance_uuid=select(
                  [instances.c.uuid],
                  instances.c.id == instance_actions.c.instance_id)
          ).execute()
      except Exception:
          uuid_column.drop()
          raise
  
      instance_actions.c.instance_id.drop()
  
  
  def downgrade(migrate_engine):
      meta.bind = migrate_engine
      instance_actions = _get_table('instance_actions')
      instances = _get_table('instances')
      id_column = Column('instance_id', Integer, ForeignKey('instances.id'))
      id_column.create(instance_actions)
  
      try:
          instance_actions.update().values(
              instance_id=select(
                  [instances.c.id],
                  instances.c.uuid == instance_actions.c.instance_uuid)
          ).execute()
      except Exception:
          id_column.drop()
          raise
  
      instance_actions.c.instance_uuid.drop()
  
subject: Remove code in migration 064 to drop an fkey that does not exist. Fixes LP bug #907878.