Item does not delete if 0

Question

an item does not delete when it its quantity is 0 and it keeps getting negative numbers. What did I wrong, how can I solve the problem.

def post(self, request, pk):
    if 'minus' in request.POST:
        cart = Cart.objects.get(order_user=self.request.user)
        item = OrderItem.objects.get(id=pk, cart=cart)
        item.quantity=F('quantity')-1
        if item.quantity == 0:
            item.delete()
        else:
            item.save()
        print(item.quantity)

Answer 1

If you set item.quantity = F('quantity')-1 then this is not equal to 0: it is an expression F('quantity')-1.

You can check if the item is less than or equal to 1 and remove it, otherwise you can decrement it. For example with:

def post(self, request, pk):
    if 'minus' in request.POST:
        cart = Cart.objects.get(order_user=self.request.user)
        qs = OrderItem.objects.filter(id=pk, cart=cart, quantity__lte=1)
        if not qs.delete()[0]:
            OrderItem.objects.filter(
                id=pk, cart=cart
            ).update(quantity=F('quantity')-1)
        # …
    # …