docs: def add_to_category(self, category, user):
          """Add this model instance to a category.
  
          :param Category category: Category to add this object to
          :param User user: User heir who adds
          :return:
          """
          init_kwargs = {
              'category': category,
              'creator': user,
              'linked_object': self
          }
          tie = self.categories.model(**init_kwargs)  # That's a model of Tie.
          tie.save()
          return tie