code: def validate_course_run_id(self, value):
          
          enterprise_customer = self.context.get('enterprise_customer')
  
          if not enterprise_customer.catalog_contains_course(value):
              raise serializers.ValidationError(
                  'The course run id {course_run_id} is not in the catalog '
                  'for Enterprise Customer {enterprise_customer}'.format(
                      course_run_id=value,
                      enterprise_customer=enterprise_customer.name,
                  )
              )
  
          return value
docs: Validates that the course run id is part of the Enterprise Customer's catalog.