无法从中按键获取值请求.会话我用djang

Question

我想和django一起做网上商店。但我有点问题。在制作购物车的过程中，我收到错误“local variable”cart_id“referenced before assignment”中视图.py. 这是这个文件：

def cart_view(request):
    try:
        cart_id = request.session['cart_id']
        cart = Cart.objects.get(id=cart_id)
        request.session['total'] = cart.items.count()
    except:
        cart = Cart()
        cart.save()
        cart_id = cart_id
        request.session['cart_id'] = cart_id
        cart = Cart.objects.get(id=cart_id)

    categories = Category.objects.all()
    return render(request, 'cart.html', locals()) 

这是回溯

^{pr2}$

然后，我试图通过将global cart_id添加到函数cart_view来解决它，但得到了另一个错误：名称“cart_id”没有定义。 以下是新的回溯：

Traceback:

File "C:\Users\tankr\Django_projects\django_shop_2\ecomapp\views.py" in product_view
  14.       cart_id = request.session['cart_id']

File "C:\Users\tankr\Django_projects\django_shop_2\eComEnv\lib\site-packages\django\contrib\sessions\backends\base.py" in __getitem__
  54.         return self._session[key]

During handling of the above exception ('cart_id'), another exception occurred:

File "C:\Users\tankr\Django_projects\django_shop_2\eComEnv\lib\site-packages\django\core\handlers\exception.py" in inner
  34.             response = get_response(request)

File "C:\Users\tankr\Django_projects\django_shop_2\eComEnv\lib\site-packages\django\core\handlers\base.py" in _get_response
  115.                 response = self.process_exception_by_middleware(e, request)

File "C:\Users\tankr\Django_projects\django_shop_2\eComEnv\lib\site-packages\django\core\handlers\base.py" in _get_response
  113.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "C:\Users\tankr\Django_projects\django_shop_2\ecomapp\views.py" in product_view
  20.       cart_id = cart_id

Exception Type: NameError at /product/iphone-xr-128gb/
Exception Value: name 'cart_id' is not defined

Answer 1

行cart_id = cart_id没有意义，您应该使用cart.id，或者更安全的cart.pk：

def cart_view(request):
    try:
        cart_id = request.session['cart_id']
        cart = Cart.objects.get(id=cart_id)
    except (KeyError, Cart.DoesNotExist):
        cart = Cart.objects.create()
        request.session['cart_id'] = cart_id = cart.pk
        request.session['total'] = 0
    else:
        request.session['total'] = cart.items.count()
    categories = Category.objects.all()
    return render(request, 'cart.html', locals())

但是请不要使用。从软件设计的角度来看，这不是一个好的实践。这意味着您知道传递给模板的内容。如果您要以酸的方式创建一个与上下文处理器中的变量同名的变量，那么您可能会得到不想要的行为。在

Answer 2

问题是try块没有执行，execept块在cart_id = cart_id出现的地方开始执行，这就是为什么会出现错误。在

您可以在现有代码中执行类似的操作

def cart_view(request):
    cart_id = request.session['cart_id']                     # before try block
    try:
        cart = Cart.objects.get(id=cart_id)
        request.session['total'] = cart.items.count()
    except:
        cart = Cart()
        cart.save()
        cart_id = cart_id
        request.session['cart_id'] = cart_id
        cart = Cart.objects.get(id=cart_id)

    categories = Category.objects.all()
    return render(request, 'cart.html', locals())