Не видит slug

from __future__ import unicode_literals
from django.db import models
from django.db.models.signals import pre_save
from django.urls import reverse
 
 
class Product(models.Model):
    category = models.ForeignKey('Category', on_delete=models.PROTECT)# к какому калькулятору относиться 
    title = models.CharField(max_length=120)# наименование материала
    quantity_or_meter = models.DecimalField(max_digits=9, decimal_places=2)
    price = models.DecimalField(max_digits=9, decimal_places=2)
    def __str__(self):
        return self.title
 
    def get_absolute_url(self):
        return reverse('product_detail', kwargs={'product_slug': self.slug})
 
class Category(models.Model):
    name= models.CharField(max_length=100)
    def __str__(self):
        return self.name
 
    def get_absolute_url(self):
        return reverse('category_detail', kwargs={'category_slug': self.slug})

from django.contrib import admin
from django.conf.urls import include, url
from ecomapp.views import index, login_view, base, table
from django.conf import settings
from django.conf.urls.static import static
 
 
urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^$', login_view, name='index'),
    url(r'^base/$', base, name='base'),
    url(r'^', include('ecomapp.urls'))
    
]
if settings.DEBUG:
    urlpatterns+= static(settings.STATIC_URL, document_root=settings.STATIC_ROOT)
    urlpatterns+= static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)