Вложение Django RelatedManager для доступа к вложенным полям

Question

Models.py

class Order(models.Model):
    order_name = models.CharField(max_length=10,unique = True, default = "")

class LineItem(models.Model):
    order = models.ForeignKey(Order, on_delete=models.CASCADE, null=True, related_name="items")
    product = models.ForeignKey(Product, on_delete=models.CASCADE,null=True, related_name="prod")
    quantity = models.IntegerField(default = 0) 

class Product(models.Model):
    product_name = models.CharField(max_length=10)
    product_price = models.DecimalField(max_digits=10,decimal_places=2) 

Итак, я пытаюсь создать запрос APIView PUT, чтобы иметь возможность изменять содержимое заказа.Так что мой метод создания в OrderItemSerializer не работает правильно.Я новичок в Django .. def update (self, instance, validated_data):

Так что в основном я не могу выполнить эту функцию.

Это структура моего экземпляра -

{
    "order_name": "OrderA",
    "line_items": [
        {
            "product": {
                "id": 7,
                "product_name": "ProdA",
                "product_price": "23.99"
            },
            "quantity": 2,
            "product_total": 47.98
        },
        {
            "product": {
                "id": 9,
                "product_name": "ProdC",
                "product_price": "19.99"
            },
            "quantity": 23,
            "product_total": 459.77
        }
    ],
    "cart_total": 507.75
}

Serializers.py

class ProductSerializer(serializers.ModelSerializer):
    class Meta:
        model = Product
        fields = ['product_name','product_price']

class OrderSerializer(serializers.ModelSerializer):

    line_items = LineItemSerializer(many=True, source='items')

    class Meta:
        model = Order
        fields = ['order_name', 'line_items', 'cart_total']

    def create(self, request):
        serialized = self.serializer_class(data=request.DATA)
        if serialized.is_valid():
            serialized.save()
            return Response(status=HTTP_202_ACCEPTED)
        else:
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

class LineItemSerializer(serializers.ModelSerializer):
    class Meta:
        model = LineItem
        depth =1
        fields = ('product', 'quantity', 'product_total')

Views.py

class LineItemList(APIView):

    def get(self,request):
        lineitemlist = LineItem.objects.all()
        serializer = LineItemSerializer(lineitemlist,many = True)
        return Response(serializer.data)

    def put(self, request):
        snippet = LineItem.objects.all()
        serializer = LineItemSerializer(snippet, data=request.data, partial = True)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def delete(self, request, order_name):
        snippet = self.get_object(order_name)
        snippet.delete()
        return Response(status=status.HTTP_204_NO_CONTENT)

class OrderList(APIView):

    def get_object(self, order_name):
        try:
            return Order.objects.get(order_name=order_name)
        except Order.DoesNotExist:
            raise Http404

    def get(self,request):
        orderlist = Order.objects.all()
        serializer = OrderSerializer(orderlist,many = True)
        return Response(serializer.data)

    def post(self, request):
        serializer = OrderSerializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def put(self, request):
        body_unicode = request.body.decode('utf-8')
        body = json.loads(body_unicode)
        order_name = body['order_name']
        snippet = Order.objects.get(order_name=order_name)
        serializer = OrderSerializer(snippet, data=request.data, partial = True)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def delete(self, request):
        body_unicode = request.body.decode('utf-8')
        body = json.loads(body_unicode)
        order_name = body['order_name']
        snippet = self.get_object(order_name)
        snippet.delete()

class OrderDetail(APIView):

    def get_object(self, order_name):
        try:
            return Order.objects.get(order_name=order_name)
        except Order.DoesNotExist:
            raise Http404

    def get(self, request, order_name):
        snippet = Order.objects.get(order_name=order_name)
        serializer = OrderSerializer(snippet)
        return Response(serializer.data) 

Проблема заключается вчто если я использую RelatedManager (ссылка на line_items из экземпляра, я не могу идти дальше).У меня есть только возможность выбора между продуктом, количеством и идентификаторами. Метод обновления, с которым я борюсь,

def update(self, instance, validated_data):
    listitems = instance.items.get(product_name = validated_data.get("product_name"))
    items = instance.items.return_set(validated_data.get("product_name"))

    items = instance.objects.items.all().select_related('product').select_related('product_name')
    items = items.product_name
    instance.save()
    a = items.get('product_name'= validated_data.get("product_name")

    asper= key.get(product_name=validated_data.get("product_name"))

    items.product.get(produc_name=validated_data.get("product_name")
    for prod in items.product.all():
        if prod.product_name==validated_data.get("product_name"):
            prod.quantity = validated_data.get("quantity")
            prod.save()
    return instance