title: Django AttributeError 'ModelFormOptions' object has no attribute 'concrete_fields'
body: <p>I get an AttributeError saying  <code>'ModelFormOptions' object has no attribute 'concrete_fields'</code>. My code is as follow:</p>
  
  <p>My model is like this:</p>
  
  <pre><code>class OrderReceiving(models.Model):
      user = models.ForeignKey(User)
      po = models.ForeignKey(Order)
      datetime = models.DateTimeField(default=timezone.now)
      product = models.ForeignKey(Product)
      quantity = models.IntegerField(default=0)
      building = models.ForeignKey(BuildingNumber)
      isele_abc = models.ForeignKey(IseleAbc)
      isele_num = models.ForeignKey(IseleNum)
      isele_floor = models.ForeignKey(IseleFloor)
  </code></pre>
  
  <p>My ModelForm is like this:</p>
  
  <pre><code>class OrderReceivingForm(ModelForm):
  
      class Meta:
          model = OrderReceiving
          exclude = ['user', 'datetime']
          labels = {
              'po': _('Vendor PO ID'),
          }
  </code></pre>
  
  <p>and my view is:</p>
  
  <pre><code>class OrderReceivingView(View):
      template = 'poreceiving/po_receive.html'
  
      def get(self, request, *args, **kwargs):
          context = {}
          form = OrderReceivingForm()
          context['form'] = form
          return render_to_response(self.template,
                                RequestContext(request, context))
  
      def post(self, request, *args, **kwargs):
          receive_form = OrderReceivingForm(request.POST)
          if receive_form.is_valid():
              receive_form.save()
          else:
              context = {}
              form = OrderReceivingForm(instance=receive_form)
              context['form'] = form
              return render_to_response(self.template,
                                    RequestContext(request, context))
          return HttpResponse('Hi everyone')
  </code></pre>
  
  <p>Here when I post invalid form then I get</p>
  
  <pre><code>AttributeError   'ModelFormOptions' object has no attribute 'concrete_fields'.
  </code></pre>
  
  <p>I expect to get form with error message.
  Please help me out.</p>
  
  <p>My Traceback:</p>
  
  <pre><code>Traceback:
  File "/home/student/virtualenvs/alex/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/student/virtualenvs/alex/lib/python2.7/site-packages/django/views/generic/base.py" in view
  71.             return self.dispatch(request, *args, **kwargs)
  File "/home/student/virtualenvs/alex/lib/python2.7/site-packages/django/views/generic/base.py" in dispatch
  89.         return handler(request, *args, **kwargs)
  File "/home/student/git/ezoffer-pos2/poreceiving/views.py" in post
  42.             form = OrderReceivingForm(instance=receive_form)
  File "/home/student/virtualenvs/alex/lib/python2.7/site-packages/django/forms/models.py" in __init__
  320.             object_data = model_to_dict(instance, opts.fields,    opts.exclude)
  File "/home/student/virtualenvs/alex/lib/python2.7/site-packages/django/forms/models.py" in model_to_dict
  132.     for f in chain(opts.concrete_fields, opts.virtual_fields, opts.many_to_many):
  
  Exception Type: AttributeError at /po/receiving/
  Exception Value: 'ModelFormOptions' object has no attribute   'concrete_fields'
  </code></pre>