code: def get_url(self, obj, view_name, request, format):
          
          # Unsaved objects will not yet have a valid URL.
          if hasattr(obj, 'pk') and obj.pk is None:
              return None
  
          lookup_value = getattr(obj, self.lookup_field)
          kwargs = {self.lookup_url_kwarg: lookup_value}
          return self.reverse(view_name, kwargs=kwargs, request=request, format=format)
docs: Given an object, return the URL that hyperlinks to the object.
  
          May raise a `NoReverseMatch` if the `view_name` and `lookup_field`
          attributes are not configured to correctly match the URL conf.