Django文件上传不起作用

<form method="post" enctype="multipart/form-data">
    {% csrf_token %}
    {{ form.as_p }}
   <button type="submit">Submit</button>
</form>

def upload_file(request):
    if request.method == 'POST':
        form = UploadFileForm(request.POST, request.FILES)
        if form.is_valid():
            file = request.FILES['file']
            # 处理文件
            return redirect('success')
    else:
        form = UploadFileForm()
    return render(request, 'upload.html', {'form': form})

# models.py
class Document(models.Model):
    file = models.FileField(upload_to='documents/')

# forms.py
class UploadFileForm(forms.ModelForm):
    class Meta:
        model = Document
        fields = ['file']

# settings.py
MEDIA_URL = '/media/'
MEDIA_ROOT = os.path.join(BASE_DIR, 'media')