如何通过 Django 模型进行查询并在没有 ManyToMany 关系的情况下访问另一个 Django 模型？

Question

I have a model called WatchList with an object called listing which corresponds to the Listings Model through a Foreign Key. I want to be able to query through the WatchList Model to get all the listings on a user's particular watchlist and display all the objects of all the listings on a webpage. I do not want to do this using a ManyToMany Field because I just got a different part of my web application that deals with the WatchList Model to work. Is there any other way to do this?

views.py

def watchlist(request):
    watchlists = WatchList.objects.filter(user=request.user)
    for listing in watchlists.listing:
        listings_needed = watchlists.listing()
    watchlist_listing = watchlists.get(listing)
    listings = Listings.objects.all().filter(watchlist_listing)
    return render(request, "auctions/watchlist.html",{
        "listings": listings
    })

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):
    listing = models.ForeignKey(Listings, on_delete=models.CASCADE, default="")
    user = models.ForeignKey(User, on_delete=models.CASCADE, default="")

This error is also occurring with the current code:

arg, value = filter_expr
TypeError: cannot unpack non-iterable function object

This error is caused by watchlist_listing = watchlists.get(listing) .

I also tried using a for loop, but that didn't work.

Answer 1

You can get all Listings for a User where there is an entry in the WatchList model by following the relationship backwards in a Listings queryset - Listings.objects.filter(watchlist__user=user)

def watchlist(request):
    listings = Listings.objects.filter(watchlist__user=request.user)
    return render(request, "auctions/watchlist.html",{
        "listings": listings
    })