为什么“model”对象不可迭代？

Question

我正在尝试在我的管理面板中仅添加一个单选按钮。我使用了多对多字段来连接另一个模型（Background）的对象。

现在的情况是：单选按钮已经存在并且可以在管理面板上工作，但是当我保存更改时，会出现错误：“'Background'对象不可迭代”。

如何才能把所选信息保存起来？

MyApp/models.py

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)
    ...

MyApp/forms.py

class FormOneForm(forms.ModelForm):
    class Meta:
        model = FormOne
        fields = ['name', 'background']

    background = forms.ModelChoiceField(widget=forms.RadioSelect, queryset=Background.objects.all(), required=False)

MyApp/admin.py

class FormOneAdmin(ModelAdmin):
    fields = ['name', 'background']
    form = FormOneForm


site.register(Background)
site.register(FormOne, FormOneAdmin)

我无法调试这个问题，希望能知道它是从哪里出现的并且如何解决它？

编辑：

附加 TraceBack：

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

- Wick Johnny

---

请发布完整的堆栈跟踪。 - Jean-François Fabre

@Jean-FrançoisFabre 我添加了跟踪追踪。 - Wick Johnny

Answer 1

你不能使用 radio widget 来创建 多对多 的关系，因为 Django 在你提交数据到 FormOneAdmin 添加视图时期望一个 background id 数组（这就是 Django 在你的堆栈跟踪中抱怨的内容），而不是单个 background id。

你可以注释掉 ModelChoiceField 这一行，这样就可以让它正常工作。

class FormOneForm(forms.ModelForm):
    class Meta:
        model = FormOne
        fields = ['name', 'background']

    # background = forms.ModelChoiceField(widget=forms.RadioSelect, queryset=Background.objects.all(), required=False)

或者如果你仍然需要让只有零个或一个Background对象绑定到一个FormOne对象，你应该使用ForeignKey而不是ManyToManyField。代码如下：

class FormOne(models.Model):
    name = models.CharField(max_length=40)
    # background = models.ManyToManyField(Background, blank=True)
    background = models.ForeignKey(Background, blank=True) # <-- use foreign key instead


class FormOneForm(forms.ModelForm):
    class Meta:
        model = FormOne
        fields = ['name', 'background']

    background = forms.ModelChoiceField(widget=forms.RadioSelect, queryset=Background.objects.all(), required=False)


class FormOneAdmin(admin.ModelAdmin):
    fields = ['name', 'background']
    form = FormOneForm

- Enix