docs: def filter_queryset(self, attrs, queryset):
          """
          Filter the queryset to all instances matching the given attributes.
          """
          # If this is an update, then any unprovided field should
          # have it's value set based on the existing instance attribute.
          if self.instance is not None:
              for field_name in self.fields:
                  if field_name not in attrs:
                      attrs[field_name] = getattr(self.instance, field_name)
  
          # Determine the filter keyword arguments and filter the queryset.
          filter_kwargs = {
              field_name: attrs[field_name]
              for field_name in self.fields
          }
          return queryset.filter(**filter_kwargs)