Views.py:

def add_to_cart(request, product_id):
    product = Product.objects.get(id=product_id)
    try:
        cart = Cart.objects.get(cart_id=_cart_id(request))

    except Cart.DoesNotExist:
        cart = Cart.objects.create(cart_id=_cart_id(request))
        cart.save()
    try:
        cart_item = CartItems.objects.get(product=product, cart=cart)
        cart_item += 1
        cart_item.save()
    except CartItems.DoesNotExist:
        cart_item = CartItems.objects.create(product=product, quantity=1, cart=cart)
        cart_item.save()
    return redirect('cart_app:cart_details')

字符串
我需要cart_item增加一个项目时，被添加到购物车。