text: # Copyright 2012 OpenStack Foundation
  # 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 migrate.changeset import UniqueConstraint
  from sqlalchemy import Index, MetaData, Table
  
  from nova.db.sqlalchemy import utils
  
  
  OLD_IDX_NAME = 'key_pair_user_id_name_idx'
  UC_NAME = 'key_pairs_uniq_name_and_user_id'
  TABLE_NAME = 'key_pairs'
  UC_COLUMNS = ['user_id', 'name', 'deleted']
  
  
  def upgrade(migrate_engine):
      meta = MetaData(bind=migrate_engine)
      key_pairs = Table(TABLE_NAME, meta, autoload=True)
      utils.drop_old_duplicate_entries_from_table(migrate_engine,
                                                  TABLE_NAME, True,
                                                  *UC_COLUMNS)
      old_idx = None
      #Drop old index because the new UniqueConstraint can be used instead.
      for index in key_pairs.indexes:
          if index.name == OLD_IDX_NAME:
              index.drop()
              old_idx = index
  
      #index.drop() in SQLAlchemy-migrate will issue a DROP INDEX statement to
      #the DB but WILL NOT update the table metadata to remove the `Index`
      #object. This can cause subsequent calls like drop or create constraint
      #on that table to fail.The solution is to update the table metadata to
      #reflect the now dropped column.
      if old_idx:
          key_pairs.indexes.remove(old_idx)
      uc = UniqueConstraint(*(UC_COLUMNS), table=key_pairs, name=UC_NAME)
      uc.create()
  
  
  def downgrade(migrate_engine):
      utils.drop_unique_constraint(migrate_engine, TABLE_NAME, UC_NAME,
                                   *(UC_COLUMNS))
      meta = MetaData(bind=migrate_engine)
      key_pairs = Table(TABLE_NAME, meta, autoload=True)
      Index(OLD_IDX_NAME, key_pairs.c.user_id,
            key_pairs.c.name).create(migrate_engine)
  