code: def related_items_changed(self, instance, related_manager):
          
          assigned = related_manager.select_related("keyword")
          keywords = " ".join([str(a.keyword) for a in assigned])
          string_field_name = list(self.fields.keys())[0] % \
                              self.related_field_name
          if getattr(instance, string_field_name) != keywords:
              setattr(instance, string_field_name, keywords)
              instance.save()
docs: Stores the keywords as a single string for searching.