docs: def check_unique(self):
          """Check the service's name and location are unique"""
          errors = []
          service_id = getattr(self, 'id', None)
          fields = [('location', views.service_location),
                    ('name', views.service_name)]
  
          for field, view in fields:
              value = getattr(self, field, None)
              if not value:
                  continue
  
              result = yield view.values(key=value)
              matched = {x['id'] for x in result if x['id'] != service_id}
              if matched:
                  errors.append("Service with {} '{}' already exists"
                                .format(field, value))
  
          if errors:
              raise exceptions.ValidationError(errors)