@classmethod
def changed(cls, entity, blob, old_value, new_value):
    """Perform any actions necessary after this attribute's value changes.

        This will be called by the blob after the value of this attribute
        has changed, override it to do any necessary post-setter actions.

        :param entity: The entity this attribute is on
        :param DataBlob blob: The blob that changed
        :param old_value: The previous value
        :param new_value: The new value
        :returns None:

        """
