NoReverseMatch at /NewListing - python-3.x

Question

I have a form on my webpage for users to create a new listing. The form loads up okay but on submission an error comes up:
NoReverseMatch at /NewListing
Reverse for 'listing' with keyword arguments '{'listing': None}' not found. 1 pattern(s) tried: ['(?P<listing_id>[0-9]+)$']
The form does save the new listing and update the homepage with the new listing but I would like that once the listing is submitted, the user is taken to the new listing page and I can't seem to get that to work without this error popping up.
models.py
class Category(models.Model):
group = models.CharField(max_length=20)
def __str__(self):
return f"{self.group}"
class Listing(models.Model):
title = models.CharField(max_length=64)
description = models.TextField(max_length=64)
price = models.DecimalField(max_digits=9, decimal_places=2, validators=[MinValueValidator(0.99)])
image = models.URLField(max_length=200, blank=True)
category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name="categories")
def __str__(self):
return f"Product: {self.title} \nDescription: {self.description} \nCurrent Price: £{self.price}\nImage: {self.image} \nCategory: {self.category}"
forms.py
class NewListingForm(forms.ModelForm):
class Meta:
model = Listing
fields = ["title", "description", "price", "image", "category"]
title = forms.CharField(widget=forms.TextInput(attrs={'autocomplete':'off'}))
description = forms.CharField(widget=forms.TextInput(attrs={'autocomplete':'off'}))
price = forms.DecimalField(label='Starting Bid Price (£)')
image = forms.URLField(widget=forms.URLInput(attrs={'autocomplete':'off'}))
views.py
def listing(request, listing_id):
listing = Listing.objects.get(pk=listing_id)
return render(request, "auctions/listingPage.html", {
"listing": listing
})
def newListing(request):
if request.method == "POST":
form = NewListingForm(request.POST)
if form.is_valid():
title = form.cleaned_data['title']
description = form.cleaned_data['description']
price = form.cleaned_data.get('price')
image = form.cleaned_data['image']
category = form.cleaned_data['category']
listing = Listing(title=title, description=description, price=price, image=image, category=category)
form.save()
return HttpResponseRedirect(reverse("listing", kwargs={'listing': listing.id}))
else:
return render(request, "auctions/newListing.html", {
"form": form,
})
else:
form = NewListingForm()
return render(request, "auctions/newListing.html", {
"form": form
})
urls.py
urlpatterns = [
path("", views.index, name="index"),
path("login", views.login_view, name="login"),
path("logout", views.logout_view, name="logout"),
path("register", views.register, name="register"),
path("<int:listing_id>", views.listing, name="listing"),
path("NewListing", views.newListing, name="newListing")
]

Answer 1

You're making a new Listing by hand from the form data, but never saving it, so it never gets an ID.
As a result, the URL that your code tries to compute as the redirection destination uses None instead of an integer for the listing ID, which blows up, because it's expecting an integer ID.
(You also save the modelform, but you don't do anything with the data that returns.)
Instead of this:
listing = Listing(title=title, description=description, price=price,image=image, category=category)
form.save()
Try just:
listing = form.save()
to let the ModelForm do all the heavy lifting and return saved object with an ID because it's in the database - that's what model forms are there for :o) https://docs.djangoproject.com/en/3.1/topics/forms/modelforms/#the-save-method