MultiValueDictKeyError when editing inline admin object

Question

I am designing a simple MCQ application using the ManyToOne relationship from django website, django version 1.6.1. I have an inline admin form which supposedly allows me to add / edit answers to a given question from the same changeform. However, if after saving a question with its answers once, i am unable to edit / add answers from the same form and get a MultiValueDictKeyError. My models are:

class SBA (models.Model):
question = models.TextField(blank=False)
system = models.CharField(max_length=3, choices=pacscon.System.which_system)
case = models.ForeignKey('pacscon.Patient')
created = models.DateField(auto_now_add=True)
reference = models.TextField(blank=True)

def __unicode__(self):
    return self.question


class Answer(models.Model):
id = models.AutoField(primary_key=True)
body = models.TextField()
correct = models.BooleanField(default=False)
sba = models.ForeignKey(SBA, null=True)

def __unicode__(self):
    return self.body

the admin.py looks like this :

from models import Answer, SBA, Mnemonic
#from django import forms
from django.contrib import admin


class AnswerInline(admin.StackedInline):
    model = Answer
    extra = 2

class SBAAdmin(admin.ModelAdmin):
        fieldsets = (
            (None, {
                'fields': ('question', 'system', 'case', 'reference')
            }),
        )
        inlines = [
            AnswerInline,
        ]
        readonly_fields = ('created',)

admin.site.register(SBA, SBAAdmin)
admin.site.register(Answer)
admin.site.register(Mnemonic)

And the error message is :

MultiValueDictKeyError at /admin/knowledge/sba/1/


Traceback:
File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  114.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in wrapper
  432.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  99.                     response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/views/decorators/cache.py" in _wrapped_view_func
  52.         response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/sites.py" in inner
  198.             return view(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapper
  29.             return bound_func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  99.                     response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in bound_func
  25.                 return func(self, *args2, **kwargs2)
File "/usr/local/lib/python2.7/dist-packages/django/db/transaction.py" in inner
  339.                 return func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in change_view
  1229.             if all_valid(formsets) and form_validated:
File "/usr/local/lib/python2.7/dist-packages/django/forms/formsets.py" in all_valid
  415.         if not formset.is_valid():
File "/usr/local/lib/python2.7/dist-packages/django/forms/formsets.py" in is_valid
  292.         err = self.errors
File "/usr/local/lib/python2.7/dist-packages/django/forms/formsets.py" in errors
  267.             self.full_clean()
File "/usr/local/lib/python2.7/dist-packages/django/forms/formsets.py" in full_clean
  314.             form = self.forms[i]
File "/usr/local/lib/python2.7/dist-packages/django/utils/functional.py" in __get__
  49.         res = instance.__dict__[self.func.__name__] = self.func(instance)
File "/usr/local/lib/python2.7/dist-packages/django/forms/formsets.py" in forms
  133.         forms = [self._construct_form(i) for i in xrange(self.total_form_count())]
File "/usr/local/lib/python2.7/dist-packages/django/forms/models.py" in _construct_form
  848.         form = super(BaseInlineFormSet, self)._construct_form(i, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/forms/models.py" in _construct_form
  564.             pk = self.data[pk_key]
File "/usr/local/lib/python2.7/dist-packages/django/utils/datastructures.py" in __getitem__
  301.             raise MultiValueDictKeyError(repr(key))

Exception Type: MultiValueDictKeyError at /admin/knowledge/sba/1/
Exception Value: "u'answer_set-0-id'"

I have searched similar requests on google and stackoverflow and my django package is fully upto date (including admin inline templates as suggested in some other answers). Will appreciate any help. Thanks

P.S This is almost certainly a bug because I can replicate the problem on official django "Polls" tutorial which uses a similar ManyToOne relationship model.

Answer 1

In Django <= 1.7.3, I needed to change the primary key field of my model to AutoField:

wrong:

class Answer(models.Model):
    id = IntegerField(primary_key=True)

correct:

class Answer(models.Model):
    id = AutoField(primary_key=True)

See https://code.djangoproject.com/ticket/15665

Answer 2

I have similar issue which was solved by update django-grappelli. If you did not use it, check your packages maybe you find what can affect work of admin site.

pip freeze | grep django- will show you current packages with versions