new_contents: # Copyright 2016 OpenStack Foundation.
  #
  # 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.
  
  """add_unique_keys_for_non_locking_model
  
  Revision ID: 015
  Revises: 014
  Create Date: 2016-08-08 11:05:20.109380
  
  """
  
  # revision identifiers, used by Alembic.
  revision = '015'
  down_revision = '014'
  
  from alembic import op
  import sqlalchemy as sa
  
  
  def upgrade():
      op.add_column(
          'delayed_calls_v2',
          sa.Column('unique_key', sa.String(length=80), nullable=True)
      )
      op.create_unique_constraint(
          None,
          'delayed_calls_v2',
          ['unique_key', 'processing']
      )
  
      op.add_column(
          'task_executions_v2',
          sa.Column('unique_key', sa.String(length=80), nullable=True)
      )
      op.create_unique_constraint(
          None,
          'task_executions_v2',
          ['unique_key']
      )
  
subject: Add unique keys for non locking model