()
Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.
Run migrations in 'online' mode.
Run migrations in online mode .
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.

    """

    # this callback is used to prevent an auto-migration from being generated
    # when there are no changes to the schema
    # reference: http://alembic.zzzcomputing.com/en/latest/cookbook.html
    def process_revision_directives(context, revision, directives):
        if getattr(config.cmd_opts, 'autogenerate', False):
            script = directives[0]
            if script.upgrade_ops.is_empty():
                directives[:] = []
                logger.info('No changes in schema detected.')

    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=target_metadata,
                      compare_type=True,
                      process_revision_directives=process_revision_directives,
                      **current_app.extensions['migrate'].configure_args)

    try:
        with context.begin_transaction():
            context.run_migrations()
    finally:
        connection.close()
def run_migrations_online ( ) : # this callback is used to prevent an auto-migration from being generated # when there are no changes to the schema # reference: http://alembic.zzzcomputing.com/en/latest/cookbook.html def process_revision_directives ( context , revision , directives ) : if getattr ( config . cmd_opts , 'autogenerate' , False ) : script = directives [ 0 ] if script . upgrade_ops . is_empty ( ) : directives [ : ] = [ ] logger . info ( 'No changes in schema detected.' ) 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 = target_metadata , compare_type = True , process_revision_directives = process_revision_directives , * * current_app . extensions [ 'migrate' ] . configure_args ) try : with context . begin_transaction ( ) : context . run_migrations ( ) finally : connection . close ( )