django-mptt ValueError: Cannot use None as a query value - django

Question

I'm using django-mptt to create catalog Category model and I'm getting an error when i'm trying to create first instance of Category model
>>> c = Category(name='cat1', slug='cat1')
>>> c.save()
Error:
ValueError at /admin/catalog/category/add/
Cannot use None as a query value
This error appears only if i don't point 'parent' field in Category instance
class TimeStampedModel(models.Model):
"""
Abstract class for adding 'create' and 'modified' info
"""
created = models.DateTimeField(auto_now_add=True)
modified = models.DateTimeField(auto_now=True)
class Meta:
abstract = True
#python_2_unicode_compatible
class Category(MPTTModel, TimeStampedModel):
''' Category model with MPTT storing approach '''
name = models.CharField(max_length=128)
slug = models.SlugField(max_length=50, unique=True)
description = models.TextField(blank=True)
parent = TreeForeignKey('self', null=True, blank=True, related_name='children')
is_active = models.BooleanField(default=True)
def __str__(self):
return self.name
def get_absolute_url(self):
return reverse('category', kwargs={'slug': self.slug})
class MPTTMeta:
order_insertion_by = ['id']
I can't find where error is. Have any suggestions?
Environment:
Request Method: POST
Request URL: http://127.0.0.1:8000/admin/catalog/category/add/
Django Version: 1.7.1
Python Version: 2.7.6
Installed Applications:
('django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'mptt',
'sorl.thumbnail',
'daguerre',
'home',
'utils',
'accounts',
'catalog',
'debug_toolbar')
Installed Middleware:
(u'debug_toolbar.middleware.DebugToolbarMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware')
Traceback:
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
111. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in wrapper
584. return self.admin_site.admin_view(view)(*args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
105. response = view_func(request, *args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
52. response = view_func(request, *args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/contrib/admin/sites.py" in inner
204. return view(request, *args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in add_view
1454. return self.changeform_view(request, None, form_url, extra_context)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapper
29. return bound_func(*args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
105. response = view_func(request, *args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/utils/decorators.py" in bound_func
25. return func.__get__(self, type(self))(*args2, **kwargs2)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/transaction.py" in inner
394. return func(*args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in changeform_view
1405. self.save_model(request, new_object, form, not add)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in save_model
1046. obj.save()
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/mptt/models.py" in save
824. right_sibling = opts.get_ordered_insertion_target(self, parent)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/mptt/models.py" in get_ordered_insertion_target
193. queryset = node.__class__._tree_manager.filter(filters).order_by(*order_by)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/manager.py" in manager_method
92. return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/query.py" in filter
691. return self._filter_or_exclude(False, *args, **kwargs)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/query.py" in _filter_or_exclude
709. clone.query.add_q(Q(*args, **kwargs))
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in add_q
1287. clause, require_inner = self._add_q(where_part, self.used_aliases)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in _add_q
1309. current_negated)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in _add_q
1314. current_negated=current_negated, connector=connector)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in build_filter
1142. value, lookups = self.prepare_lookup_value(value, lookups, can_reuse)
File "/home/oleshko/design/.virtualenvs/begemotik/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in prepare_lookup_value
1040. raise ValueError("Cannot use None as a query value")
Exception Type: ValueError at /admin/catalog/category/add/
Exception Value: Cannot use None as a query value

Answer 1

Trouble was here:
class MPTTMeta:
order_insertion_by = ['id']
I changed 'order_insertion_by' field to another (to 'created' in my example) and it began to work

Answer 2

I found the cause of this error by using the "node_order_by" attribute when referencing a field using auto_now in a MP_node subclass....
Class Tree(MP_Node):
name = models.CharField(max_length=45)
last_modified = models.DateTimeField(auto_now=True)
node_order_by = ['last_modified']
Commented out node_order_by or using a different field and the error went away. I think the issue is that Treebeard is trying to figure out where to insert the child record and it doesn't have a date yet for the new record.