def run_migrations_online()

in migrations/env.py [0:0]


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    engine = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix='sqlalchemy.',
        poolclass=pool.NullPool)

    connection = engine.connect()
    context.configure(
        connection=connection,
        target_metadata=DB.metadata
    )

    try:
        with context.begin_transaction():
            context.run_migrations()
    finally:
        connection.close()