new_contents: from alembic import op
  import sqlalchemy as sa
  
  
  """empty message
  
  Revision ID: 458dd2fc1172
  Revises: 8ecdd6381235
  Create Date: 2017-12-21 16:38:49.659073
  
  """
  
  # revision identifiers, used by Alembic.
  revision = '458dd2fc1172'
  down_revision = '8ecdd6381235'
  
  
  def upgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.create_table('notifications',
      sa.Column('id', sa.Integer(), nullable=False),
      sa.Column('name', sa.Text(), nullable=False),
      sa.Column('content', sa.Text(), nullable=False),
      sa.Column('created_at', sa.DateTime(), nullable=False),
      sa.PrimaryKeyConstraint('id'),
      sa.UniqueConstraint('name')
      )
      op.create_table('user_notifications',
      sa.Column('id', sa.Integer(), nullable=False),
      sa.Column('user_id', sa.Integer(), nullable=False),
      sa.Column('notification_id', sa.Integer(), nullable=False),
      sa.ForeignKeyConstraint(['notification_id'], ['notifications.id'], ondelete='CASCADE'),
      sa.ForeignKeyConstraint(['user_id'], ['users.id'], ondelete='CASCADE'),
      sa.PrimaryKeyConstraint('id'),
      sa.UniqueConstraint('user_id', 'notification_id', name='_user_notification')
      )
      # ### end Alembic commands ###
  
  
  def downgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.drop_table('user_notifications')
      op.drop_table('notifications')
      # ### end Alembic commands ###
  
subject: add migration for notification tables