问TypeError返回模型条目

EN

<class 'TypeError'> views.py 80 ("l = Listing(title=title, description=description, url=url, user=user_id, category=category)")

class NewListingForm(forms.Form):
    title = forms.CharField(max_length=200)
    description = forms.CharField(max_length=500)
    url = forms.URLField()
    bid = forms.DecimalField(decimal_places=2, max_digits=10)
    category = forms.ModelChoiceField(queryset=Category.objects.all())

def newListing(request):
    try:
        if request.method == "POST":
            newListingForm = NewListingForm(request.POST)
            if newListingForm.is_valid():
                title = newListingForm.cleaned_data['title']
                description = newListingForm.cleaned_data['description']
                url = newListingForm.cleaned_data['url']
                bid = newListingForm.cleaned_data['bid']
                category = newListingForm.cleaned_data['category']
                current_user = request.user
                user_id = current_user.id
                **l = Listing(title=title, description=description, url=url, user=user_id, category=category)**
                l.save()
                b = Bid(price=bid, bid_count=0)
                b.listing.add(l)
                b.save()
                return HttpResponseRedirect(reverse("index"))
        else:
            newListingForm = NewListingForm()
            return render(request, "auctions/newListing.html", {
                'form': newListingForm
            })
    except Exception as exc:
        exc_type, exc_obj, exc_tb = sys.exc_info()
        fname = os.path.split(exc_tb.tb_frame.f_code.co_filename)[1]
        print(exc_type, fname, exc_tb.tb_lineno)
        newListingForm = NewListingForm()
        return render(request, 'auctions/newListing.html', {
            'form': newListingForm
        })

class Listing(models.Model):
    title = models.CharField(max_length=200)
    description = models.CharField(max_length=500)
    url = models.URLField()
    user = models.ForeignKey('User', on_delete=models.CASCADE, name='author')
    category = models.ForeignKey('Category', on_delete=models.CASCADE, name='category', default="")

    def __str__(self):
        return f'{self.id}: {self.title}'

class Bid(models.Model):
    price = models.DecimalField(decimal_places=2, max_digits=10)
    bid_count = models.IntegerField()
    listing = models.ForeignKey('Listing', on_delete=models.CASCADE, name='listing', default="")

    def __str__(self):
        return f'{self.slug} ({self.price})'