Error while updating django field?

Question

Django

I'm trying to update a field in the database, but I get the error
Cannot force an update in save() with no primary key.

def zaym(request):
  if request.method == 'POST':
    status = ZaimForm(request.POST)
    if status.is_valid():
      instance = status.save(commit = False)
      instance.save(update_fields = ['status'])
    else:
      return render_to_response('sms_signup/errors.html')
  else:
    new_zaim = user_zaim.objects.all()
    status = ZaimForm()
    return render(request, 'operator/new-zaim.html', {'new_zaim':new_zaim, 'status':status})