Releases the given entity from management under the given Unit Of
        Work.

        :raises ValueError: If `entity` is not managed at all or is not
          managed by the given Unit Of Work.

def release(cls, entity, unit_of_work):
        """
        Releases the given entity from management under the given Unit Of
        Work.

        :raises ValueError: If `entity` is not managed at all or is not
          managed by the given Unit Of Work.
        """
        if not hasattr(entity, '__everest__'):
            raise ValueError('Trying to unregister an entity that has not '
                             'been registered yet!')
        elif not unit_of_work is entity.__everest__.unit_of_work:
            raise ValueError('Trying to unregister an entity that has been '
                             'registered with another session!')
        delattr(entity, '__everest__')