@classmethod
def _get_expected_attrs(cls, context, *args, **kwargs):
    """Return expected attributes when getting a cluster.

        Expected attributes depend on whether we are retrieving all related
        services as well as if we are getting the services summary.
        """
    expected_attrs = []
    if kwargs.get('get_services'):
        expected_attrs.append('services')
    if kwargs.get('services_summary'):
        expected_attrs.extend(('num_hosts', 'num_down_hosts'))
    return expected_attrs
