Как посчитать сумму в serializer drf?

Question

[DoggieMurr]

models.py

class Cart(models.Model):
    uuid = models.UUIDField(default=uuid.uuid4)
    product = models.ForeignKey(Product,
                                on_delete=models.CASCADE,
                                null=False,
                                blank=False)
    user = models.ForeignKey(User,
                             on_delete=models.CASCADE,
                             null=False,
                             blank=False,
                             related_name='cart')
    quantity = models.IntegerField(null=False, blank=False, default=1)
    amount = models.IntegerField(null=True, blank=True)

    def save(self, *args, **kwargs):
        self.amount = (self.product.total_price * self.quantity)
        return super().save(*args, **kwargs)

serializer.py

class CartSerializer(ModelSerializer):
    product = CartProductSerializer(read_only=True)
    cart_amount = IntegerField()

    class Meta:
        model = Cart
        fields = ('product', 'quantity', 'amount', 'cart_amount')

views.py

class CartView(ListAPIView):
    serializer_class = CartSerializer
    permission_classes = [IsAuthenticated]

    def get_queryset(self):
        user = self.request.user
        return Cart.objects.filter(user=user).annotate(
            cart_amount=Sum('amount')
        )

response

[
    {
        "product": {
            "title": "bmw",
            "total_price": 1099
        },
        "quantity": 2,
        "amount": 2198,
        "cart_amount": 2198
    },
    {
        "product": {
            "title": "new prod",
            "total_price": 11000
        },
        "quantity": 22,
        "amount": 242000,
        "cart_amount": 242000
    }
]

desire response

[
    {
        "product": {
            "title": "bmw",
            "total_price": 1099
        },
        "quantity": 2,
        "amount": 2198
    },
    {
        "product": {
            "title": "new prod",
            "total_price": 11000
        },
        "quantity": 22,
        "amount": 242000
    },
   "cart_amount": 244198
]