此错误的原因：没有列表与给定的查询匹配

Question

用户可以通过单击添加按钮将该产品添加到观察列表中，然后添加按钮将更改为 Rimo。这次单击此按钮，该产品将从列表中删除。主页上应该有一个链接，点击它会显示监视列表中的所有产品，点击详细按钮可以看到该产品的详细信息，点击删除按钮，您可以将它们从列表中删除。

当我单击按钮时，它向我发送此错误。 怎么了？

Page not found (404)
No List matches the given query.
Request Method: GET
Request URL:    http://127.0.0.1:8000/add/?productid=1
Raised by:  auctions.views.add
Using the URLconf defined in commerce.urls, Django tried these URL patterns, in this 
order:

admin/
[name='index']
login [name='login']
logout [name='logout']
register [name='register']
product_detail/<int:product_id>/ [name='product_detail']
watchlist/<str:username> [name='watchlist']
add/ [name='add']
The current path, add/, matched the last one.

views.py：

@login_required(login_url="login")
def watchlist(request, username):
    products = Watchlist.objects.filter(user = username)
    return render(request, 'auctions/watchlist.html', {'products': products})


@login_required(login_url="login")
def add(request):
    product_id = request.POST.get('productid', False)
    watch = Watchlist.objects.filter(user = request.user.username)

    for items in watch:
        if int(items.watch_list.id) == int(product_id):
            return watchlist(request, request.user.username)


    watch_list = get_object_or_404(List, pk = product_id)
    user = request.user.username
    context = {
        'watch_list': watch_list,
        'user': user
    }
    new_watch = get_object_or_404(Watchlist, context)
    new_watch.save()


    messages.success(request, "Item added to watchlist")
    return product_detail(request, product_id)




@login_required(login_url="login")
def remove(request):
    remove_id = request.GET["productid"]
    list_ = Watchlist.objects.get(pk = remove_id)
    messages.success(request, f"{list_.watch_list.title} is deleted from your 
           watchlist.")
    list_.delete()
    return redirect("index")

urls.py：

path("product_detail/<int:product_id>/", views.product_detail, 
  name="product_detail"),
path('watchlist/<str:username>', views.watchlist, name='watchlist'),
path('add/', views.add, name='add'),
path('remove/', views.remove, name='remove'),

whatchlist.html：

{% extends "auctions/layout.html" %}
{% block body %}

    {% if products %}
        {% for product in products %}
            <img src= {{ item.image.url }} alt = "{{item.title}}"><br>
            <a>{{ item.title }}</a><br>
            <a>{{ item.category }}</a><br>
            <a><a>Frist Bid: </a> {{ item.first_bid }} $ </a><br>

            <a href="{% url 'product_detail' item.id %}">View Product</a>

            <form action="{% url 'remove' product.id %}" method="post">
                {% csrf_token %}
                <button type="submit">Remove</button>
            </form>
        {% endfor %}
    {% else %}
        <p>No products in watchlist</p>
    {% endif %}

{% endblock %}

product_detail.html（相关部分）：

<form method= "get" action = "{% url 'add' %}">
    <button type = "submit" value = {{ product.id }}  name = "productid" >Add to 
       Watchlist</button>
</form>

layout.html（相关部分）：

    <li class="nav-item">
            <a class="nav-link" href="{% url 'index' %}">Active Listings</a>
    </li>

    <li class="nav-item">
            <a class="nav-link" href="{% url 'category' %}">Category</a>
    </li>

    <li class="nav-item">
            <a class="nav-link" href="{% url 'watchlist' user.username %}">My 
                WatchList</a>
    </li>

此文件（layout.html）在页面顶部创建标题，可以通过单击每个标题来访问这些标题。这样，点击关注列表，就会显示列表中的产品。目前，点击此链接不会显示“关注列表中的产品”。

Answer 1

<form method="post" action="{% url 'add' %}">  <button type="submit" value="{{ product.id }}" name="productid">Add to  Watchlist</button> </form>

或

product_id = request.GET.get('productid', False)