我有两个模型

class MenuItem(models.Model):
    title = models.CharField(max_length=255, db_index=True)
    price = models.DecimalField(max_digits=6, decimal_places=2, db_index=True)
    featured = models.BooleanField(db_index=True)
    category = models.ForeignKey(Category, on_delete=models.PROTECT)
    def __str__(self):
        return f'{self.title}'

class Cart(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    menuitem = models.ForeignKey(MenuItem, on_delete=models.CASCADE)
    quantity = models.SmallIntegerField()
    unit_price = models.DecimalField(max_digits=6, decimal_places=2, default=0)
    price = models.DecimalField(max_digits=6, decimal_places=2, default=0)

    class Meta:
        unique_together = ('menuitem', 'user')

对于特定对象，MenuItem.price应该等于Cart.unit_price。现在我遇到的问题是为Cart模型编写序列化程序。
到目前为止，我已经尝试了这个：

class MenuItemSerializer(serializers.HyperlinkedModelSerializer):
    title = serializers.CharField(max_length=255)
    price = serializers.DecimalField(max_digits=6, decimal_places=2)
    category_id = serializers.IntegerField(write_only=True)
    category = CategorySerializer(read_only=True)
    featured = serializers.BooleanField()    
    class Meta:
        model = MenuItem
        fields = ['title', 'price', 'category', 'category_id', 'featured']
        depth = 1

class CartSerializer(serializers.ModelSerializer):
    user = serializers.HiddenField(
        default=serializers.CurrentUserDefault(),
    )
    menu_item = MenuItemSerializer
    quantity = serializers.IntegerField()
    # unit_price = serializers.DecimalField(max_digits=6, decimal_places=2, style={'input_type':'hidden'})
    unit_price = serializers.ReadOnlyField(source="menuitem.price", read_only=True)
    price = SerializerMethodField()
    class Meta:
        model = Cart
        fields = ['user', 'menuitem', 'unit_price', 'quantity', 'price']

    def get_price(self, obj):
        return obj.quantity * obj.unit_price

然后相关视图

class Cart(mixins.ListModelMixin,
           mixins.DestroyModelMixin,
           generics.GenericAPIView):
    queryset = Cart.objects.all()
    serializer_class = CartSerializer

    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)
    
    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)
    
    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)

但是，这不会返回所需的价格值。它只返回0。
我是一个django新手，这让我抓狂。如果有人能帮忙就好了。
这是我得到的一个示例响应：{“menuitem”：1，“unit_price”：2.5、“数量”：3、“价格”：0 }