Cannot set the discount to zero for a user without the 'can_give_discount' permission

I am having trouble trying to get this to work. The attached code under the form_valid method is my attempt to this challenge. But the error reports that a user without the right permission created a discounted product. Is there any way to resolve this issue?

products/models.py from django.core.urlresolvers import reverse from django.db import models

class Product(models.Model): name = models.CharField(max_length=255) description = models.TextField() price = models.DecimalField() discount = models.DecimalField(blank=True, null=True)

class Meta:
    permissions = (
        ('can_give_discount','gives discount'),
    )

def __str__(self):
    return self.name

def get_absolute_url(self):
    return reverse("products:detail", kwargs={"pk": self.pk})

products/views.py from django.contrib.auth.mixins import LoginRequiredMixin from django.views import generic

from . import models

class List(generic.ListView): model = models.Product

class Detail(generic.DetailView): model = models.Product

class Create(LoginRequiredMixin, generic.CreateView): fields = ("name", "description", "discount", "price") model = models.Product

def form_valid(self, form):
    if(not self.request.user.has_perm('model.can_give_discount')):
        self.object = form.save()
        self.object.discount = 0
        return HttpResponseRedirect(self.get_success_url())