old_contents: # Copyright 2013 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.
  #
  # vim: tabstop=4 shiftwidth=4 softtabstop=4
  
  from migrate.changeset import UniqueConstraint
  from sqlalchemy import MetaData, Table
  
  from nova.db.sqlalchemy import utils
  
  
  UC_NAME = 'uniq_aggregate_metadata0aggregate_id0key0deleted'
  COLUMNS = ('aggregate_id', 'key', 'deleted')
  TABLE_NAME = 'aggregate_metadata'
  
  
  def upgrade(migrate_engine):
      meta = MetaData(bind=migrate_engine)
      t = Table(TABLE_NAME, meta, autoload=True)
  
      utils.drop_old_duplicate_entries_from_table(migrate_engine, TABLE_NAME,
                                                  True, *COLUMNS)
      uc = UniqueConstraint(*COLUMNS, table=t, name=UC_NAME)
      uc.create()
  
  
  def downgrade(migrate_engine):
      utils.drop_unique_constraint(migrate_engine, TABLE_NAME, UC_NAME, *COLUMNS)
  
new_contents: # Copyright 2013 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.
  #
  # vim: tabstop=4 shiftwidth=4 softtabstop=4
  
  from migrate.changeset import UniqueConstraint
  from migrate import ForeignKeyConstraint
  from sqlalchemy import MetaData, Table
  
  from nova.db.sqlalchemy import utils
  
  
  UC_NAME = 'uniq_aggregate_metadata0aggregate_id0key0deleted'
  COLUMNS = ('aggregate_id', 'key', 'deleted')
  TABLE_NAME = 'aggregate_metadata'
  
  
  def upgrade(migrate_engine):
      meta = MetaData(bind=migrate_engine)
      t = Table(TABLE_NAME, meta, autoload=True)
  
      utils.drop_old_duplicate_entries_from_table(migrate_engine, TABLE_NAME,
                                                  True, *COLUMNS)
      uc = UniqueConstraint(*COLUMNS, table=t, name=UC_NAME)
      uc.create()
  
  
  def downgrade(migrate_engine):
      if migrate_engine.name == 'mysql':
          # NOTE(jhesketh): MySQL Cannot drop index
          # 'uniq_aggregate_metadata0aggregate_id0key0deleted': needed in a
          # foreign key constraint. So we'll remove the fkey constraint on the
          # aggregate_metadata table and add it back after the index is
          # downgraded.
          meta = MetaData(bind=migrate_engine)
          table = Table('aggregate_metadata', meta, autoload=True)
          ref_table = Table('aggregates', meta, autoload=True)
          params = {'columns': [table.c['aggregate_id']],
                    'refcolumns': [ref_table.c['id']],
                    'name': 'aggregate_metadata_ibfk_1'}
          fkey = ForeignKeyConstraint(**params)
          fkey.drop()
  
      utils.drop_unique_constraint(migrate_engine, TABLE_NAME, UC_NAME, *COLUMNS)
  
      if migrate_engine.name == 'mysql':
          fkey.create()
  
subject: Fix migration 211 to downgrade with MySQL