此错误的原因：没有列表与给定查询匹配

问：

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。这一次，通过单击此按钮，该产品将从列表中删除。 主页上应该有一个链接，点击它，就会显示观察列表中的所有产品，点击详情按钮，可以看到产品的详细信息，点击删除按钮，可以将它们从列表中删除。

models.py

class User(AbstractUser):
    pass


class List(models.Model):
    choice = (
        ('d', 'Dark'),
        ('s', 'Sweet'),
    )
    user = models.CharField(max_length=64)
    title = models.CharField(max_length=64)
    description = models.TextField()  
    category = models.CharField(max_length=64)      
    first_bid = models.IntegerField()  
    image = models.ImageField(upload_to="img/", null=True)      
    image_url = models.CharField(max_length=228, default = None, blank = True, null = 
             True)
    status = models.CharField(max_length=1, choices= choice)
    active_bool = models.BooleanField(default = True)

class Watchlist(models.Model):
    user = models.CharField(max_length=64)
    watch_list = models.ForeignKey(List, on_deleted= 
                models.CASCADE)

views.py：

def product_detail(request, product_id):
    product = get_object_or_404(List, pk=product_id)
    comments = Comment.objects.filter(product=product)

    if request.method == 'POST':
    
        # comment
        if 'comment' in request.POST:
            user = request.user
            if user.is_authenticated:
                content = request.POST.get('content')
                comment = Comment(product=product, user=user, content=content)
                comment.save()
    

    context = {
        'product': product,
        'comments': comments, 
       }

    return render(request, 'auctions/product_detail.html', context)



 @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, productid):
     #watch = Watchlist.objects.filter(user = 
              #request.user.username)
      watchlist_product = get_object_or_404(Watchlist, 
                          pk=productid)

     for items in watchlist_product:
        if int(items.watch_list.id) == int(productid):
            return watchlist(request, request.user.username)
    
    product = get_object_or_404(List, 
               pk=watchlist_product.watch_list)
   new_watch = Watchlist(product, user = request.user.username)
   new_watch.save()
   messages.success(request, "Item added to watchlist")
   return product_detail(request, productid)




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

product_deyail.html（仅与问题相关的部分）：

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

监视列表.html：

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

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

            <a href="{% url 'product_detail' product.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 %}

layout.html（仅与问题相关的部分 & 显示链接名称）：

<ul class="nav">
        <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 'watchlist' 
                  user.username %}">My WatchList</a>
        </li>


        {% if user.is_authenticated %}
            <li class="nav-item">
                <a class="nav-link" href="{% url 'logout' %}">Log Out</a>
            </li>
        {% else %}
            <li class="nav-item">
                <a class="nav-link" href="{% url 'login' %}">Log In</a>
            </li>
            <li class="nav-item">
                <a class="nav-link" href="{% url 'register' %}">Register</a>
            </li>
        {% endif %}

urls.py：

path('watchlist/<str:username>', views.watchlist, 
      name='watchlist'),
path('add/<int:productid>', views.add, name='add'),
path('remove/<int:pid>', views.remove, name='remove'),

错误： 反转“product_detail”，未找到参数“（''，）”。尝试了 1 种模式： ['product_detail/（？P<product_id>[0-9]+）/\Z']

监视列表.html：

<a href="{% url 'product_detail' product_id %}">View Product</a>