Wagtail 0.8.6 - admin - NoneType' object has no attribute 'allowed_subpage_types'

Question

I'm using Wagtail 0.8.6 with Django 1.7.7, when I try to access to a specific page in the admin:

http://127.0.0.1:8020/admin/pages/4/

I get the following error:

AttributeError at /admin/pages/4/
'NoneType' object has no attribute 'allowed_subpage_types'

this is the traceback:

Environment:


Request Method: GET
Request URL: http://127.0.0.1:8020/admin/pages/4/

Django Version: 1.7.7
Python Version: 2.7.3
Installed Applications:
('django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'raven.contrib.django.raven_compat',
 'compressor',
 'taggit',
 'modelcluster',
 'django.contrib.admin',
 'preventconcurrentlogins',
 'django_medusa',
 'wagtail.wagtailcore',
 'wagtail.wagtailadmin',
 'wagtail.wagtaildocs',
 'wagtail.wagtailsnippets',
 'wagtail.wagtailusers',
 'wagtail.wagtailimages',
 'wagtail.wagtailembeds',
 'wagtail.wagtailsearch',
 'wagtail.wagtailredirects',
 'wagtail.contrib.wagtailmedusa',
 'myapp',
 'django_extensions')
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 'preventconcurrentlogins.middleware.PreventConcurrentLoginsMiddleware',
 'wagtail.wagtailcore.middleware.SiteMiddleware',
 'wagtail.wagtailredirects.middleware.RedirectMiddleware')


Template error:
In template /home/vagrant/venv/local/lib/python2.7/site-packages/wagtail/wagtailadmin/templates/wagtailadmin/pages/list.html, error at line 265
   'NoneType' object has no attribute 'allowed_subpage_types'
   255 :                         {% if allow_navigation %}


   256 :                             {% if moving %}


   257 :                                 {% if page.can_descend %}


   258 :                                     <a href="{% url 'wagtailadmin_pages_move_choose_destination' page_to_move.id page.id %}" class="icon text-replace icon-arrow-right navigate-pages" title="{% blocktrans with title=page.title %}Explorer subpages of '{{ title }}'{% endblocktrans %}">{% trans 'Explore' %}</a>


   259 :                                 {% endif %}


   260 :                             {% elif choosing %}


   261 :                                 {% if page.can_descend %}


   262 :                                     <a href="{% url 'wagtailadmin_choose_page_child' page.id %}?{{ querystring }}" class="icon text-replace icon-arrow-right navigate-pages" title="{% blocktrans with title=page.title %}Explorer subpages of '{{ title }}'{% endblocktrans %}">{% trans 'Explore' %}</a>


   263 :                                 {% endif %}


   264 :                             {% else %}


   265 :                                  {% if page.is_navigable %} 


   266 :                                     <a href="{% url 'wagtailadmin_explore' page.id %}" class="icon text-replace icon-arrow-right" title="{% blocktrans with title=page.title %}Explore child pages of '{{ title }}'{% endblocktrans %}">{% trans "Explore" %}</a>


   267 :                                 {% elif page_perms.can_add_subpage %}


   268 :                                     <a href="{% url 'wagtailadmin_pages_add_subpage' page.id %}" class="icon text-replace icon-plus-inverse" title="{% blocktrans with title=page.title %}Add a child page to '{{ title }}'{% endblocktrans %}">{% trans 'Add subpage' %}</a>


   269 :                                 {% endif %}


   270 :                             {% endif %}


   271 :                         {% endif %}


   272 :                      </td>


   273 :                 </tr>


   274 :             {% endfor %}


   275 :         {% else %}


Traceback:
File "/home/vagrant/venv/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/vagrant/venv/local/lib/python2.7/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  21.                 return view_func(request, *args, **kwargs)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/wagtail/wagtailadmin/views/pages.py" in index
  65.         'pages': pages,
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/shortcuts.py" in render
  50.     return HttpResponse(loader.render_to_string(*args, **kwargs),
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader.py" in render_to_string
  178.         return t.render(context_instance)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  148.             return self._render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  126.         return compiled_parent._render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  65.                 result = block.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  65.                 result = block.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  150.                 return template.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  148.             return self._render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in _render
  142.         return self.nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  312.                 return nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  201.                             nodelist.append(node.render(context))
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  312.                 return nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  312.                 return nodelist.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in render
  844.                 bit = self.render_node(node, context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  80.             return node.render(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  305.                     match = condition.eval(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/defaulttags.py" in eval
  898.         return self.value.resolve(context, ignore_failures=True)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in resolve
  596.                 obj = self.var.resolve(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in resolve
  734.             value = self._resolve_lookup(context)
File "/home/vagrant/venv/local/lib/python2.7/site-packages/django/template/base.py" in _resolve_lookup
  788.                             current = current()
File "/home/vagrant/venv/local/lib/python2.7/site-packages/wagtail/wagtailcore/models.py" in can_add_subpage
  1269.         if not self.page.specific_class.allowed_subpage_types():  # this page model has an empty subpage_types list, so no subpages are allowed

Exception Type: AttributeError at /admin/pages/4/
Exception Value: 'NoneType' object has no attribute 'allowed_subpage_types'

before the upgrade, with Wagtail 0.5 and Django 1.6.5 was working. Any idea of what can cause that?

Answer 1

Thanks! I solved that by:

from wagtail.wagtailcore.models import Page
pages = Page.objects.all()
for p in pages:
    if not p.specific_class:
        p.delete()

Answer 2

I hit this bug today as well.

I found this line of code in the wagtailcore models.py file and added a print statement to narrow down which page was causing the issue.

def can_add_subpage(self):
   print self

From there I checked the wagtailcore_page table in the database and found the specific page. In my case it was pointing to a content type for a model that was no longer being used and I updated the database accordingly.

You can also test this out in the shell.

from wagtail.wagtailcore.models import Page
pages = Page.objects.all()
for p in pages:
    if not p.specific_class:
        print p

I've seen this happen often in CMS's, you create a page of a certain type and and then delete/rename the model but the old data stays in the page tree. I always try to make sure I have deleted those content types in the CMS first, before removing the code.

Hopefully this will point you in the right direction. Wagtail on.