new_contents: """empty message
  
  Revision ID: 818f7bda2528
  Revises: bf1347acdee2
  Create Date: 2018-04-10 22:45:19.462757
  
  """
  from alembic import op
  import sqlalchemy as sa
  
  
  # revision identifiers, used by Alembic.
  revision = '818f7bda2528'
  down_revision = 'bf1347acdee2'
  branch_labels = None
  depends_on = None
  
  
  def upgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.add_column('preview_file', sa.Column('path', sa.String(length=400), nullable=True))
      # ### end Alembic commands ###
  
  
  def downgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.drop_column('preview_file', 'path')
      # ### end Alembic commands ###
  
subject: Add migration file for preview path field