text: # Copyright 2019 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.
  #
  
  from alembic import op
  import sqlalchemy as sa
  from sqlalchemy.engine import reflection
  
  
  """ovn backend
  
  Revision ID: f4b9654dd40c
  Revises: 86274d77933e
  Create Date: 2019-11-25 13:09:31.367837
  
  """
  
  # revision identifiers, used by Alembic.
  revision = 'f4b9654dd40c'
  down_revision = '86274d77933e'
  
  OVN_REVISION_NUMBERS = 'ovn_revision_numbers'
  OVN_HASH_RING = 'ovn_hash_ring'
  
  
  def upgrade():
      inspector = reflection.Inspector.from_engine(op.get_bind())
      table_names = inspector.get_table_names()
      if OVN_REVISION_NUMBERS in table_names and OVN_HASH_RING in table_names:
          op.alter_column(OVN_REVISION_NUMBERS, 'revision_number',
                          nullable=False, server_default='0',
                          existing_type=sa.BIGINT(), existing_nullable=False)
          return
  
      op.create_table(
          OVN_REVISION_NUMBERS,
          sa.Column('standard_attr_id', sa.BigInteger, nullable=True),
          sa.Column('resource_uuid', sa.String(36), nullable=False, index=True),
          sa.Column('resource_type', sa.String(36), nullable=False, index=True),
          sa.Column('revision_number', sa.BigInteger, nullable=False,
                    server_default='0'),
          sa.Column('created_at', sa.DateTime, nullable=False,
                    default=sa.func.now()),
          sa.Column('updated_at', sa.TIMESTAMP, default=sa.func.now(),
                    onupdate=sa.func.now(), nullable=True),
          sa.ForeignKeyConstraint(
              ['standard_attr_id'], ['standardattributes.id'],
              ondelete='SET NULL'),
          sa.PrimaryKeyConstraint('resource_uuid', 'resource_type')
      )
  
      op.create_table(
          OVN_HASH_RING,
          sa.Column('node_uuid', sa.String(36), nullable=False, index=True),
          sa.Column('group_name', sa.String(length=256), nullable=False,
                    index=True),
          sa.Column('hostname', sa.String(length=256), nullable=False),
          sa.Column('created_at', sa.DateTime, nullable=False,
                    default=sa.func.now()),
          sa.Column('updated_at', sa.DateTime, nullable=False,
                    default=sa.func.now()),
          sa.PrimaryKeyConstraint('node_uuid', 'group_name'),
      )
  