A node may not be made a child of any of its descendants in django mptt

Question

here is the models.py

 class Category(MPTTModel):
            title = models.CharField(max_length =120)
            name = models.CharField(max_length=120)
            parent = models.ForeignKey('self' , null = True , blank = True ,     verbose_name='parent category', related_name='categories')
            description = models.TextField(null=True , blank=True)
            active = models.BooleanField(default=True)
            slug = models.SlugField(blank=True)
            timestamp = models.DateTimeField(auto_now_add=True , auto_now=False)


            def get_absolute_url(self):
                    return reverse('categories', kwargs={'path': self.get_path()})



 class Product(MPTTModel):
            brand = models.ForeignKey(Brand , related_name='products')
            category = models.ForeignKey('Category', verbose_name='categories', related_name='products' , default='')
            parent = models.ForeignKey('self' , related_name = 'children' , null=True , blank=True)
            title = models.CharField(max_length=500)
            gender = models.CharField(max_length=10 , choices=GENDER_CHOICES)
            SKU = models.CharField(max_length=255 , blank=True ,  unique=True)
            description = models.TextField(max_length = 500 ,blank=True ,null=True)
            price = models.IntegerField()
            color = models.CharField(max_length=120)
            discount = models.IntegerField(blank=True ,null =True)
            active = models.BooleanField(default=True)
            is_related = models.BooleanField(default=False)
            is_combo = models.BooleanField(default=False)
            is_verified = models.BooleanField(default=False)
            in_stock = models.BooleanField(default=False)
            slug = models.SlugField(max_length=255 , blank=True , unique=True)
            timestamp = models.DateTimeField(auto_now_add=True,auto_now=False)

            objects = ProductManager()

            class Meta:
                    unique_together = ('SKU', 'slug', 'category', 'brand')

            def __unicode__(self):
                return self.title

whenever i try to make a product with some parent it throws this error

 A node may not be made a child of any of its descendants.

here is the traceback

  Traceback:

        File "C:\Python27\lib\site-packages\django\core\handlers\base.py" in get_response
          132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
        File "C:\Python27\lib\site-packages\django\contrib\admin\options.py" in wrapper
          616.                 return self.admin_site.admin_view(view)(*args, **kwargs)
        File "C:\Python27\lib\site-packages\django\utils\decorators.py" in _wrapped_view
          110.                     response = view_func(request, *args, **kwargs)
        File "C:\Python27\lib\site-packages\django\views\decorators\cache.py" in _wrapped_view_func
          57.         response = view_func(request, *args, **kwargs)
        File "C:\Python27\lib\site-packages\django\contrib\admin\sites.py" in inner
          233.             return view(request, *args, **kwargs)
        File "C:\Python27\lib\site-packages\django\contrib\admin\options.py" in add_view
          1516.         return self.changeform_view(request, None, form_url, extra_context)
        File "C:\Python27\lib\site-packages\django\utils\decorators.py" in _wrapper
          34.             return bound_func(*args, **kwargs)
        File "C:\Python27\lib\site-packages\django\utils\decorators.py" in _wrapped_view
          110.                     response = view_func(request, *args, **kwargs)
        File "C:\Python27\lib\site-packages\django\utils\decorators.py" in bound_func
          30.                 return func.__get__(self, type(self))(*args2, **kwargs2)
        File "C:\Python27\lib\site-packages\django\utils\decorators.py" in inner
          145.                     return func(*args, **kwargs)
        File "C:\Python27\lib\site-packages\django\contrib\admin\options.py" in changeform_view
          1467.                 self.save_model(request, new_object, form, not add)
        File "C:\Python27\lib\site-packages\django\contrib\admin\options.py" in save_model
          1078.         obj.save()
        File "C:\Python27\lib\site-packages\mptt\models.py" in save
          973.             super(MPTTModel, self).save(*args, **kwargs)
        File "C:\Python27\lib\site-packages\django\db\models\base.py" in save
          710.                        force_update=force_update, update_fields=update_fields)
        File "C:\Python27\lib\site-packages\django\db\models\base.py" in save_base
          747.                                    update_fields=update_fields, raw=raw, using=using)
        File "C:\Python27\lib\site-packages\django\dispatch\dispatcher.py" in send
          201.             response = receiver(signal=self, sender=sender, **named)
        File "C:\Users\lenovo\Desktop\Grooved2\grooved\src\products\models.py" in product_post_save_receiver
          403.          instance.save()
        File "C:\Python27\lib\site-packages\mptt\models.py" in save
          918.                                 self, parent, 'last-child', save=False)
        File "C:\Python27\lib\site-packages\mptt\managers.py" in _move_node
          576.                     self._move_root_node(node, target, position)
        File "C:\Python27\lib\site-packages\mptt\managers.py" in _move_root_node
          1190.             raise InvalidMove(_('A node may not be made a child of any of its descendants.'))

        Exception Type: InvalidMove at /admin/products/product/add/
        Exception Value: A node may not be made a child of any of its descendants.

how can i solve the above problem.Thanks in Advance

Answer 1

From this issue comments, running rebuild() method can solve the problem.

from .models import MyModel

MyModel.objects.rebuild()