code: def get_related(self, instance, number):
          
          cache = self.cache
          cache_key = '%s:%s' % (instance.pk, number)
          if cache_key not in cache:
              related_objects = super(CachedModelVectorBuilder,
                                      self).get_related(instance, number)
              cache[cache_key] = related_objects
              self.cache = cache
          return cache[cache_key]
docs: Implement high level cache system for get_related.