实例：

$quote = $this->quoteRepository->getActive($result->getQuoteId());
            $quoteItem = $quote->getItemById($result->getItemId());
            $price = (float)$quoteItem->getProduct()->getPrice() - (float)$upsellInfo->getDiscount();
            $quoteItem->setCustomPrice($price);
            $quoteItem->setOriginalCustomPrice($price);
            $quoteItem->getProduct()->setIsSuperMode(true);
            $quoteItem->save();
            $quote->save();
            $this->quoteRepository->save($quote);
            return $quote->getItemById($result->getItemId());