无法通过 WatchList 实例访问管理器如何解决此错误？

skateb2020 发表于 Dev

滑板2020

我正在尝试通过 Django 创建一个电子商务网站（CS50 项目 2），并拥有一个具有多种形式的 Django 视图。在这个视图中，我试图在 Django 表单中使用布尔字段来使用户能够将列表添加到他的监视列表中，这两个都是模型。在尝试这样做时，我收到了上述错误。

部分views.py

def listing(request, id):
    #gets listing
    listing = Listings.objects.get(id=id)
    watchlist_form = WatchListForm()
    if request.method == "POST":
        watchlist_form = WatchListForm(request.POST)
        if watchlist_form.is_valid():
            watchlist = watchlist_form.save(commit=False)
            watchlist.user = request.user
            watchlist.add_to_watchlist = True
            new_watchlist_listing = watchlist.objects.listings.add(listing) 
            return render(request, "auctions/listing.html",{
                "auction_listing": listing,
                "watchlistForm": watchlist_form
            })
        else:
            return render(request, "auctions/listing.html",{
                "auction_listing": listing,
                "form": comment_form,
                "comments": comment_obj,
                "bidForm": bid_form,
                "bids": bid_obj,
                "watchlistForm": watchlist_form
            })
    return render(request, "auctions/listing.html",{
        "auction_listing": listing,
        "form": comment_form,
        "comments": comment_obj,
        "bidForm": bid_form,
        "bids": bid_obj,
        "watchlistForm": watchlist_form
    })

models.py

class Listings(models.Model):
    CATEGORY = [
    ("Miscellaneous", "Miscellaneous"),
    ("Movies and Television", "Movies and Television"),
    ("Sports", "Sports"),
    ("Arts and Crafts", "Arts and Crafts"),
    ("Clothing", "Clothing"),
    ("Books", "Books"),
]
    title = models.CharField(max_length=64)
    description = models.CharField(max_length=500)
    bid = models.DecimalField(max_digits=1000000000000, decimal_places=2)
    image = models.URLField(null=True, blank=True)
    category = models.CharField(max_length=64, choices=CATEGORY, default=None)
    user = models.ForeignKey(User, on_delete=models.CASCADE, default="")


class WatchList(models.Model):
    listings = models.ManyToManyField(Listings)
    user = models.ForeignKey(User, on_delete=models.CASCADE, default="")
    add_to_watchlist = models.BooleanField(default=False)

错误信息

raise AttributeError("Manager isn't accessible via %s instances" % cls.__name__)
AttributeError: Manager isn't accessible via WatchList instances

由于这一行而发生此错误：new_watchlist_listing = watchlist.objects.listings.add(listing)。

威廉·范昂森

您添加带有的元素，因此没有该部分。因此，您的视图应如下所示：modelobject.manytomanyfield.add()~~.objects~~

from django.contrib.auth.decorators import login_required
from django.shortcuts import get_object_or_404, redirect

@login_required
def listing(request, id):
    listing = get_object_or_404(Listings.objects, pk=id)
    watchlist_form = WatchListForm()
    if request.method == "POST":
        watchlist_form = WatchListForm(request.POST)
        if watchlist_form.is_valid():
            watchlist_form.instance.user = request.user
            watchlist_form.instance.add_to_watchlist = True
            watchlist = watchlist_form.save()
            watchlist.listings.add(listing)
            return redirect('name-of-the-view')
    return render(request, 'auctions/listing.html',{
        'auction_listing': listing,
        'form': comment_form,
        'comments': comment_obj,
        'bidForm': bid_form,
        'bids': bid_obj,
        'watchlistForm': watchlist_form
    })

注意：通常最好使用^[Django-doc]，然后直接使用^[Django-doc]。如果对象不存在，例如因为用户自己更改了 URL，则将导致返回HTTP 404 Not Found响应，而 using将导致HTTP 500 Server Error。get_object_or_404(…) .get(…) get_object_or_404(…).get(…)

注意：如果 POST 请求成功，您应该制作一个^[Django-doc]来实现Post/Redirect/Get模式 ^[wiki]。这样可以避免在用户刷新浏览器时发出相同的 POST 请求。redirect

注意：您可以使用@login_required装饰器 ^[Django-doc]将视图限制为经过身份验证的用户的视图。

注意：通常最好不要在使用方法 ^[Django-doc]commit=False保存表单时使用：这将阻止保存多对多关系，因为只有在提交项目时才能保存这些关系。通常最好更改表单中的包裹。有关更多信息，请参阅我的文章 ^{[Django-antipatterns]}。.save(…).instance