title: Why 'model' object is not iterable?
body: <p>I'm trying to add a radioselect in my admin panel <strong>only</strong>. I use a many to many field in order to connect objects of another model (Background). </p>
  
  <p><em>What I have now :</em> The radio select is here and works on the admin panel, but I get this error when I proceed and save the changes : <code>'Background' object is not iterable</code>.</p>
  
  <p>How can I save and keep the information as selected ?</p>
  
  <p>MyApp/<strong>models.py</strong></p>
  
  <pre><code>class Background(models.Model):
      bk_color = models.CharField(max_length=20)
      ...
  
  class FormOne(models.Model):
      name = models.CharField(max_length=40)
      background = models.ManyToManyField(Background, blank=True)
      ...
  </code></pre>
  
  <p>MyApp/<strong>forms.py</strong></p>
  
  <pre><code>class FormOneForm(forms.ModelForm):
      class Meta:
          model = FormOne
          fields = ['name', 'background']
  
      background = forms.ModelChoiceField(widget=forms.RadioSelect, queryset=Background.objects.all(), required=False)
  </code></pre>
  
  <p>MyApp/<strong>admin.py</strong></p>
  
  <pre><code>class FormOneAdmin(ModelAdmin):
      fields = ['name', 'background']
      form = FormOneForm
  
  
  site.register(Background)
  site.register(FormOne, FormOneAdmin)
  </code></pre>
  
  <p>I couldn't debug the problem, I'd be glad to know from where it is coming and how I can resolve it ?</p>
  
  <p>EDIT :</p>
  
  <p>Added TraceBack : </p>
  
  <pre><code>Traceback:
  File "C:\Python34\lib\site-packages\django\core\handlers\base.py" in get_response
    132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Python34\lib\site-packages\django\contrib\admin\options.py" in wrapper
    618.                 return self.admin_site.admin_view(view)(*args, **kwargs)
  File "C:\Python34\lib\site-packages\django\utils\decorators.py" in _wrapped_view
    110.                     response = view_func(request, *args, **kwargs)
  File "C:\Python34\lib\site-packages\django\views\decorators\cache.py" in _wrapped_view_func
    57.         response = view_func(request, *args, **kwargs)
  File "C:\Python34\lib\site-packages\django\contrib\admin\sites.py" in inner
    233.             return view(request, *args, **kwargs)
  File "C:\Python34\lib\site-packages\django\contrib\admin\options.py" in change_view
    1521.         return self.changeform_view(request, object_id, form_url, extra_context)
  File "C:\Python34\lib\site-packages\django\utils\decorators.py" in _wrapper
    34.             return bound_func(*args, **kwargs)
  File "C:\Python34\lib\site-packages\django\utils\decorators.py" in _wrapped_view
    110.                     response = view_func(request, *args, **kwargs)
  File "C:\Python34\lib\site-packages\django\utils\decorators.py" in bound_func
    30.                 return func.__get__(self, type(self))(*args2, **kwargs2)
  File "C:\Python34\lib\contextlib.py" in inner
    30.                 return func(*args, **kwds)
  File "C:\Python34\lib\site-packages\django\contrib\admin\options.py" in changeform_view
    1470.                 self.save_related(request, form, formsets, not add)
  File "C:\Python34\lib\site-packages\django\contrib\admin\options.py" in save_related
    1102.         form.save_m2m()
  File "C:\Python34\lib\site-packages\django\forms\models.py" in save_m2m
    102.                 f.save_form_data(instance, cleaned_data[f.name])
  File "C:\Python34\lib\site-packages\django\db\models\fields\related.py" in save_form_data
    2603.         setattr(instance, self.attname, data)
  File "C:\Python34\lib\site-packages\django\db\models\fields\related.py" in __set__
    1266.         value = tuple(value)
  
  Exception Type: TypeError at /admin/multistepform/formone/75/
  Exception Value: 'Background' object is not iterable
  </code></pre>