Why is this if statement not working in Django?

Question

I'm just trying to run an if statement in html using django in the {% %} things. The statemnet is {% if listing in watchlist %}. Even though the listing is in watchlists, it doesn't make the if statement true.

I used {{ }} to see what watchlist and listing are. for {{ watchlist }} I got: <QuerySet [<Watchlists: 15: Dan1308 has added 3: The Bus (yes the cool airplane), starting at 3000 to watchlist>]>

for {{ listing }} I got: 3: The Bus (yes the cool airplane), starting at 3000

here's my views.py:

def listing(request, NewListings_id):
user = request.user
listing = NewListings.objects.get(pk=NewListings_id)
comments = Comments.objects.filter(listing=listing)
watchlist = Watchlists.objects.filter(user=user)
return render(request, "auctions/listing.html", {
    "listing": listing,
    "comments": comments,
    "user": user,
    "watchlist": watchlist
})

and here's my models.py:

class Watchlists(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
listing = models.ForeignKey(NewListings, on_delete=models.CASCADE)

def __str__(self):
    return f"{self.id}: {self.user} has added {self.listing} to watchlist"

So, why is it not working?

Answer 1

watchlist = Watchlists.objects.filter(user=user)
listing = NewListings.objects.get(pk=NewListings_id)

listing is a NewListings instance, and watchlist is a queryset of Watchlists instances. So listing isn't in the queryset.

Instead, there is a watchlist instance in the queryset, where the listing foreign key points to listing .

A different approach would be to check whether the listing is in the watchlist in the view:

def listing(request, NewListings_id):
    user = request.user
    listing = NewListings.objects.get(pk=NewListings_id)
    comments = Comments.objects.filter(listing=listing)
    watchlist = Watchlists.objects.filter(user=user)
    listing_in_watchlist = Watchlist.objects.filter(user=user, listing=listing).exists()
    return render(request, "auctions/listing.html", {
        "listing": listing,
        "comments": comments,
        "user": user,
        "watchlist": watchlist,
        "listing_in_watchlist": listing_in_watchlist,
    })

Now, in the template, you can use {% if listing_in_watchlist %} .