title: Using TabularInline in Django Admin
body: <p>I am trying to show the <code>orderitemsadmin</code> in the <code>orderadmin</code> using TabularInline but I keep getting different errors like the following error.</p>
  <pre><code>AttributeError: 'OrderItemAdmin' object has no attribute 'urls'
  </code></pre>
  <p>and</p>
  <pre><code>django.core.exceptions.ImproperlyConfigured: AUTH_USER_MODEL refers to model 'auth.User' that has not been installed
  </code></pre>
  <p>This is a Django e-commerce project and I am trying to facilitating the admin viewing the orders and their items.</p>
  <p>I don't have much experience in using TabularInline that is why I am not able to do it corrrectly or what might be the mistake that I am doing.</p>
  <p>Here is the admin.py</p>
  <pre><code>class OrderItemAdmin(admin.TabularInline):
      list_display = ['item', 'quantity', 'ordered']
      model = OrderItem
      raw_id_fields = ['item']
  
  
  class OrderAdmin(admin.ModelAdmin):
      list_display = ['user', 'ordered', 'ordered_date', 'coupon', 'payment', 'shipping_address', 'status',
                      'refund_requested', 'refund_granted', 'ref_code']
      inlines = [
          OrderItemAdmin,
      ]
  admin.site.register(OrderItem, OrderItemAdmin)
  admin.site.register(Order, OrderAdmin)
  </code></pre>
  <p>Here is the models.py</p>
  <pre><code>class OrderItem(models.Model):
      item = models.ForeignKey(Item, on_delete=models.CASCADE)
  
  class Order(models.Model):
      items = models.ManyToManyField(OrderItem)
  </code></pre>