code: def get_one(slug):
      
      item = Product.objects.published()\
          .prefetch_related(Prefetch("paramvalue_set", queryset=ParamValue.objects.published().order_by('sort').prefetch_related("param")))\
          .filter(slug=slug).first()
      return item
docs: Возвращает один товар
      :param slug: символьный код товара
      :return: