Django：模型不是从模型表单创建的

Question

我尝试从模型表单创建新对象，但不保存对象。

models.py

class VideoFile(models.Model):
    name = models.CharField(max_length=200, blank=True)
    file = models.FileField(upload_to="video/", validators=[validate_file_extension])

forms.py

class VideoCreateForm(ModelForm): 

    class Meta:
        model = VideoFile
        fields = ['name', 'file']

views.py

def add_video(request):    

    if request.method == "POST":
        form = VideoCreateForm(request.POST, request.FILES)

        if form.is_valid():
            instance = form.save()
            messages.success(request, "saved") 
        else:
            messages.error(request, 'No success!.')            
        return redirect('vtv:video') 
    else:
        form = VideoCreateForm()
    return render(request, "vtv/video_add.html", {'form': form})

templates.html

<h3>Add new video</h3>
<form method = "post">
{% csrf_token %}
{{ form.as_p }}
<input type="submit" />
</form>

怎么了？