django - 在一个 Django View 上获取 "This QueryDict instance is immutable"，但在另一个 View 上却没有

Question

我有两个 View ，一个在表单无效时尝试添加到 POST 数据时工作正常，另一个在尝试执行相同操作时给出“此 QueryDict 实例是不可变的”错误。我知道这些观点太相似而无法首先存在，并计划将它们结合起来……但我想首先了解导致其中一个失败的区别是什么。

这个 View 工作正常:

@login_required
def url_parse(request):
    cu = request.user
    if request.method == 'POST':
        form = UrlBragForm(request.POST, request.FILES)
        if form.is_valid():
            t = handle_image_upload(form.cleaned_data['image'],cu.pk,'url')
            if t:
                b = Brag()
                b.user = cu
                b.image = t
                b.url = form.cleaned_data['url']
                b.description = form.cleaned_data['brag']
                b.active = True
                b.timestamp = time.time()
                b.save()
                tags = parse_tags(form.cleaned_data['brag'])
                if tags:
                    for tg in tags:
                        b.tags.add(tg)
            else:
                errors = form._errors.setdefault("image", ErrorList())
                errors.append(u"There was an issue with your image.  Please try again.")
        else:
            clean = cleanMessage(request.POST['brag'])
            if clean != 'is_clean':
                request.POST['brag'] = clean
    else:
        form = UrlBragForm()
    return render_to_response('brag/url_brag.html', {'form':form,}, context_instance=RequestContext(request))

但是当 View 无效时，尝试用“干净”数据填充 request.POST['brag'] 时，此 View 给了我一个“此 QueryDict 实例是不可变的”:

@login_required
def brag_add_image(request):
    cu = request.user
    if request.method == 'POST':
        form = ImageAddBragForm(request.POST, request.FILES)
        if form.is_valid():
            t = handle_image_upload(form.cleaned_data['image'],cu.pk,'url')
            if t:
                b = Brag()
                b.user = cu
                b.image = t
                b.description = form.cleaned_data['brag']
                b.active = True
                b.timestamp = time.time()
                b.save()
                b.url = 'http://%s%s' % (Site.objects.get_current().domain, reverse('image_display', args=(b.pk,)))
                b.save()
                tags = parse_tags(form.cleaned_data['brag'])
                if tags:
                    for tg in tags:
                        b.tags.add(tg)
            else:
                errors = form._errors.setdefault("image", ErrorList())
                errors.append(u"There was an issue with your image.  Please try again.")
        else:
            clean = cleanMessage(request.POST['brag'])
            if clean != 'is_clean':
                request.POST['brag'] = clean
    else:
        form = ImageAddBragForm()
    return render_to_response('brag/image_brag_add.html', {'form':form,}, context_instance=RequestContext(request))

这是要求的回溯:

Traceback:
File "site/src/django/django/core/handlers/base.py" in get_response
  111.                         response = callback(request, *callback_args, **callback_kwargs)
File "site/src/django/django/contrib/auth/decorators.py" in _wrapped_view
  20.                 return view_func(request, *args, **kwargs)
File "site/brag/views.py" in brag_add_image
  241.                 request.POST['brag'] = clean
File "site/src/django/django/http/__init__.py" in __setitem__
  439.         self._assert_mutable()
File "site/src/django/django/http/__init__.py" in _assert_mutable
  436.             raise AttributeError("This QueryDict instance is immutable")

Exception Type: AttributeError at /brag/brag_add_image/
Exception Value: This QueryDict instance is immutable

Answer 1

想通了。这是因为我在模板中调用表单的方式。如果将 enctype 更改为 multipart，则不会再收到错误。这绝不是一个解决方案，您应该考虑在表单类而不是 View 中执行此操作。但我想弄清楚为什么它会以一种方式起作用，而不是另一种方式。

<form action="." method="post" class="genForm" enctype="multipart/form-data">

对比

<form action="." method="post" class="genForm">

这似乎可能是 Django 中的一个错误(为什么不在这两种情况下强制执行？)

由于这个答案似乎有些困惑，我这里有一个更简单的示例，显示了相同的结果:

查看:

def testit(request):
    if request.method == "POST":
        form = testForm(request.POST, request.FILES)
        clean = 'Going to stuff post data with this string'
        if form.is_valid():
            print 'valid'
            request.POST['testOne'] = clean
        else:
            print 'not valid'
            request.POST['testOne'] = clean
    else:
        form = testForm()
    return render_to_response('brag_board/test.html', {'form':form}, context_instance=RequestContext(request))

表格:

class testForm(forms.Form):
    testOne = forms.CharField(required=True)
    testTwo = forms.CharField(required=True)

出现错误的模板:

<!DOCTYPE html>
<html>
<head>
    <title>test</title>
</head>
<body>

<form action="." method="post" class="genForm">
{{ form }}
{% csrf_token %}
<button type="submit" name="action" value="addnewsletter">test</button>
</form>

</body>
</html>

不报错的模板:

<!DOCTYPE html>
<html>
<head>
    <title>test</title>
</head>
<body>

<form action="." method="post" class="genForm" enctype="multipart/form-data">
{{ form }}
{% csrf_token %}
<button type="submit" name="action" value="addnewsletter">test</button>
</form>

</body>
</html>