base.py 文件源码

def get_max_id(cls, session):
        """Get the current max value of the ``id`` column.

        When creating and storing ORM objects in bulk, :mod:`sqlalchemy` does not automatically
        generate an incrementing primary key ``id``. To do this manually, one needs to know the
        current max ``id``. For ORM object classes that are derived from other ORM object classes,
        the max ``id`` of the lowest base class is returned. This is designed to be used with
        inheritance by joining, in which derived and base class objects have identical ``id`` values.

        Args:
            session: database session to operate in
        """
        # sqlalchemy allows only one level of inheritance, so just check this class and all its bases
        id_base = None
        for c in [cls] + list(cls.__bases__):
            for base_class in c.__bases__:
                if base_class.__name__ == 'Base':
                    if id_base is None:
                        # we found our base class for determining the ID
                        id_base = c
                    else:
                        raise RuntimeError("Multiple base object classes for class " + cls.__name__)

        # this should never happen
        if id_base is None:
            raise RuntimeError("Error searching for base class of " + cls.__name__)

        # get its max ID
        max_id = session.query(func.max(id_base.id)).scalar()

        # if no object is present, None is returned
        if max_id is None:
            max_id = 0

        return max_id