python - カテゴリ一致クエリが存在しません エラー

Question

URLを投稿してリンクモデルに保存したい。しかし、私はこのエラーが発生しました:

Category matching query does not exist

私のviews.py

def category_detail(request, category_name):
    if request.POST:
        form = CreateLinkForm(request.POST)
        user = request.user
        if form.is_valid():
            link = form.save(commit=False)
            link.user = user 
            link.category = Category.objects.get(name=category_name)
            link.save()
        return HttpResponseRedirect(reverse('category_detail', args=[category_name]))
    else:
        form = CreateLinkForm()
    links = Link.objects.filter(category__name=category_name)
    return render_to_response("category_detail.html", {"links":links, "form":form, "category_name":category_name}, context_instance=RequestContext(request))

端末の python manage.py シェルでクエリを実行すると、次のようになります。

>>> from link.models import Category
>>> Category.objects.all()
[<Category: <django.db.models.fields.related.ManyRelatedManager object at 0x22dbfd0> Programlama>, <Category: <django.db.models.fields.related.ManyRelatedManager object at 0x22de110> Foto>, <Category: <django.db.models.fields.related.ManyRelatedManager object at 0x22dbfd0> Sanat>]
>>> Category.objects.get(name="Foto")
<Category: <django.db.models.fields.related.ManyRelatedManager object at 0x22dbed0> Foto>

リンクモデル:

class Link(models.Model):
    user = models.ForeignKey(User)
    posted_at = models.DateTimeField(auto_now_add=True)
    url = models.URLField()
    title = models.CharField(max_length=255, null=True, blank=True)
    category = models.ForeignKey(Category)

    def __unicode__(self):
        return "%s %s %s" %(self.url, self.title, self.category)

リンクフォームの作成:

class CreateLinkForm(ModelForm):
    class Meta:
        model = Link 
        exclude = ["user", "posted_at", "category"]

だから私の間違っているのは何ですか？このエラーが発生した理由Category matching query does not exist