docs: def check_service(self):
          """Check the service exists and is a repository service"""
          try:
              service = yield Service.get(self.service_id)
          except couch.NotFound:
              raise exceptions.ValidationError('Service {} not found'
                                               .format(self.service_id))
  
          if service.service_type != 'repository':
              raise exceptions.ValidationError('{} is not a repository service'
                                               .format(self.service_id))
  
          if service.state != State.approved:
              raise exceptions.ValidationError('{} is not an approved service'
                                               .format(self.service_id))