如何用modelform更新django 2.1中的图像?[复制品]

嘿,我在这个网站上的第一个问题,对不起我的英语。所以我尝试在django框架中的模型上上传一个文件。

class banner(models.Model):
#id is made by Django
name = models.CharField(max_length=255)
created_by = models.CharField(max_length=255)
company = models.CharField(max_length=255)
register_date = models.DateField(auto_now_add=True)
file = models.FileField(null=True, blank=True)
file_name = models.CharField(max_length=255)

这是模型

class BannerForm(forms.Form):
name=forms.CharField(max_length=255)
created_by=forms.CharField(max_length=255)
company=forms.CharField(max_length=255)
data_type=forms.CharField(max_length=255)
register_date=forms.DateField()
file=forms.FileField()
file_name=forms.CharField(max_length=255)

这是表格

定义添加表单(请求): 表单=bannerform() last=models.banner.objects.all().last()

if request.method == "POST":
    form = forms.BannerForm(request.POST, request.FILES or None)
    if form.is_valid():
        form.cleaned_data['created_by']
        new_banner=models.banner()
        new_banner.id=last.id+1
        new_banner.name=form.cleaned_data['name']
        new_banner.register_date=form.cleaned_data['register_date']
        new_banner.company=form.cleaned_data['company']
        new_banner.file=form.cleaned_data['file']
        new_banner.file_name=new_banner.file.name
        new_banner.created_by=form.cleaned_data['created_by']
        new_banner.save()

return render(request, "add_banner.html",{"form":form})

这是视图。现在每当我试图添加一个横幅。我浏览文件,但在我按下提交后,它是必须选择的文件,就像它不识别我浏览到的表单按钮。有什么建议吗?