pickle.py

def get_instance(cls, args):
    inst = cls.query.get_raw(args)
    if inst is None:
        raise ValueError(
            "Query for type '%s' returned no items for "
            "primary key: (%s)." % (
                cls.__name__,
                ", ".join(map(repr, args))
            ))

    return inst


def get_instance_query(inst):
    return (
        get_instance,
        (type(inst), tuple(getattr(inst, name) for name in (
            column.name for column in inst.__mapper__.primary_key
        ))))


Model.__reduce__ = get_instance_query