code: def merge_link_object(serializer, data, instance):
      
  
      link_object = {}
  
      if not getattr(instance, 'pk', None):
          # If instance doesn't have a `pk` field, we'll assume it doesn't
          # have a canonical resource URL to hang a link off of.
          # This generally only affectes Ephemeral Objects.
          return data
  
      link_fields = serializer.get_link_fields()
      for name, field in six.iteritems(link_fields):
          # For included fields, omit link if there's no data.
          if name in data and not data[name]:
              continue
  
          link = getattr(field, 'link', None)
          if link is None:
              base_url = ''
              if settings.ENABLE_HOST_RELATIVE_LINKS:
                  # if the resource isn't registered, this will default back to
                  # using resource-relative urls for links.
                  base_url = DynamicRouter.get_canonical_path(
                      serializer.get_resource_key(),
                      instance.pk
                  ) or ''
              link = '%s%s/' % (base_url, name)
          # Default to DREST-generated relation endpoints.
          elif callable(link):
              link = link(name, field, data, instance)
  
          link_object[name] = link
  
      if link_object:
          data['links'] = link_object
      return data
docs: Add a 'links' attribute to the data that maps field names to URLs.
  
      NOTE: This is the format that Ember Data supports, but alternative
            implementations are possible to support other formats.