如何在django中保存多对多字段

Question

型号.py：

class Tag(models.Model):
    name = models.CharField(max_length=100)
    description = models.CharField(max_length=500, null=True, blank=True)
    created = models.DateTimeField(auto_now_add=True)
    modified = models.DateTimeField(auto_now_add=True)

class Post(models.Model):
    user = models.ForeignKey(User)
    tag = models.ManyToManyField(Tag)
    title = models.CharField(max_length=100)
    content = models.TextField()
    created = models.DateTimeField(default=datetime.datetime.now)
    modified = models.DateTimeField(default=datetime.datetime.now)

    def __unicode__(self):
        return '%s,%s' % (self.title,self.content)


class PostModelForm(forms.ModelForm):
    class Meta:
        model = Post


class PostModelFormNormalUser(forms.ModelForm):
    class Meta:
        model = Post
        widgets = { 'tag' : TextInput() }
        exclude = ('user', 'created', 'modified')

    def __init__(self, *args, **kwargs):
        super(PostModelFormNormalUser, self).__init__(*args, **kwargs)      
        self.fields['tag'].help_text = None

我在views.py中的尝试：（看起来不正确）

    if request.method == 'POST':
        form = PostModelFormNormalUser(request.POST)
        print form
        print form.errors           
        tagstring = form.data['tag']
        splitedtag = tagstring.split()

        if form.is_valid():
            temp = form.save(commit=False)
            temp.user_id = user.id
            temp.save()
            post = Post.objects.get(id=temp.id)

            l = len(splitedtag)         
            for i in range(l):
                obj = Tag(name=splitedtag[i])
                obj.save()
                post.tag.add(obj)

            post = Post.objects.get(id=temp.id)
            return HttpResponseRedirect('/viewpost/' + str(post.id))

    else:
        form = PostModelFormNormalUser()
        context = {'form':form}
        return render_to_response('addpost.html', context, context_instance=RequestContext(request))

是否有人可以完成后示例的代码编辑以保存到后表、标记表和后标记表中？

输入表单将包含一个文本框以键入“title”和“content”的texarea，以及一个文本框以字符串形式键入“tag”。标记字符串用空格分隔。我需要将这些标记词保存到标记表中，并映射到post_tag table中。

我该怎么做？