title: use Django filter but not working?
body: <p>I made a template to put some posts on it, each post has two category, I use <code>&lt;a&gt;</code> to be the options, like:</p>
  
  <pre><code>    &lt;div class="cate"&gt;
      &lt;span class="cate_span0"&gt;Species：&lt;/span&gt;
      &lt;a href="?kind={{ post_kind }}"&gt;
      &lt;span class="cate_span {% ifequal animal_kind '' %}chosen_animal{% endifequal %}"&gt;All&lt;/span&gt;
      &lt;/a&gt;
      &lt;a href="?animal=dog&amp;kind={{ post_kind }}"&gt;
      &lt;span class="cate_span {% ifequal animal_kind 'dog' %}chosen_animal{% endifequal %}"&gt;Dog&lt;/span&gt;
      &lt;/a&gt;
      &lt;a href="?animal=cat&amp;kind={{ post_kind }}"&gt;
      &lt;span class="cate_span {% ifequal animal_kind 'cat' %}chosen_animal{% endifequal %}"&gt;Cat&lt;/span&gt;
      &lt;/a&gt;
      &lt;a href="?animal=other&amp;kind={{ post_kind }}"&gt;
      &lt;span class="cate_span {% ifequal animal_kind 'other' %}chosen_animal{% endifequal %}"&gt;other&lt;/span&gt;
      &lt;/a&gt;
  &lt;br/&gt;
  
  &lt;span class="cate_span0"&gt;Article：&lt;/span&gt;
  &lt;a href="?animal={{ animal_kind }}"&gt;
  &lt;span class="cate_span {% ifequal post_kind '' %}chosen_animal{% endifequal %}"&gt;All&lt;/span&gt;
  &lt;/a&gt;
  &lt;a href="?kind=new_explorer&amp;animal={{ animal_kind }}"&gt;
  &lt;span class="cate_span {% ifequal post_kind 'new_explorer' %}chosen_animal{% endifequal %}"&gt;Stray&lt;/span&gt;
  &lt;/a&gt;
  &lt;a href="?kind=tell_story&amp;animal={{ animal_kind }}"&gt;
  &lt;span class="cate_span {% ifequal post_kind 'tell_story' %}chosen_animal{% endifequal %}"&gt;Story&lt;/span&gt;
  &lt;/a&gt;
  &lt;a href="?kind=giving&amp;animal={{ animal_kind }}"&gt;
  &lt;span class="cate_span {% ifequal post_kind 'giving' %}chosen_animal{% endifequal %}"&gt;Post&lt;/span&gt;
  &lt;/a&gt;
  &lt;a href="?kind=want&amp;animal={{ animal_kind }}"&gt;
  &lt;span class="cate_span {% ifequal post_kind 'want' %}chosen_animal{% endifequal %}"&gt;Want&lt;/span&gt;
  &lt;/a&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>And in my views I use <code>kind</code> and <code>animal</code> filter the DB:</p>
  
  <pre><code>animal_kind = request.GET.get('animal', '')
      post_kind = request.GET.get('kind', '')
      if animal_kind:
          all_posts = all_posts.filter(animal_cate=animal_kind)
      if post_kind:
          all_posts = all_posts.filter(post_cate=post_kind)
  </code></pre>
  
  <p>And:</p>
  
  <pre><code>        return render(request, 'community.html', {
          "all_posts" : posts,
          "animal_kind" : animal_kind,
          "post_kind" : post_kind,
          })
  </code></pre>
  
  <p>my models:</p>
  
  <pre><code>class Posts(models.Model):
  POST_CATE_CHOICES = [
      ('GV', 'giving'),
      ('WT', 'want'),
      ('NE', 'new_explorer'),
      ('TS', 'tell_story'),
  ]
  ANIMAL_CATE_CHOICES = [
      ('DOG', 'dog'),
      ('CAT', 'cat'),
      ('OTHER', 'other'),
  ]
  user = models.ForeignKey(UserInfo, related_name='user_name', verbose_name=u"所属用户")
  icon = models.ForeignKey(UserInfo, related_name='user_icon', verbose_name=u"用户头像")
  title = models.CharField(max_length=100, verbose_name=u"帖子标题")
  content = models.TextField(null=True, blank=True, verbose_name=u"帖子内容")
  add_time = models.DateTimeField(default=datetime.now, verbose_name=u"发帖时间")
  image = models.ImageField(max_length=100, upload_to='post_img/%Y/%m', null=True, verbose_name=u"贴图")
  post_cate = models.CharField(max_length=2, choices=POST_CATE_CHOICES, verbose_name="帖子类型")
  animal_cate = models.CharField(max_length=10, choices=ANIMAL_CATE_CHOICES, null=True, verbose_name="动物类型")
  comment_num = models.IntegerField(default=0, verbose_name=u"评论数量")
  likes = models.IntegerField(default=0, verbose_name=u"顶")
  dislikes = models.IntegerField(default=0, verbose_name=u"踩")
  </code></pre>
  
  <p>my posts:</p>
  
  <pre><code>{% for post in all_posts.object_list %}
  &lt;div class="post"&gt;
      &lt;a href="" class="user_a"&gt;
      &lt;img class="icon" src="{{ post.icon.icon.url }}"&gt;
      &lt;span class="name_span"&gt;{{ post.user.username }}&lt;/span&gt;
      &lt;/a&gt;
      &lt;span class="time"&gt;发表时间：{{ post.add_time }}&lt;/span&gt;
      &lt;span class="clicked"&gt;回复：{{ post.comment_num }}&lt;/span&gt;
      &lt;a href=""&gt;
      &lt;img class="post_img" src="{{ MEDIA_URL }}{{ post.image }}"&gt;
      &lt;div class="article"&gt;
      &lt;h3 class="title"&gt;{{ post.title }}&lt;/h3&gt;
      &lt;span class="content"&gt;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;{{ post.content }}&lt;/span&gt;
      &lt;/div&gt;
      &lt;/a&gt;
  &lt;/div&gt;
  {% endfor %}
  </code></pre>
  
  <p>It seems like only the <code>animal_kind</code>actually working and it can filter the exact item, but when I filter the <code>post_cate</code>, it's empty.
  I don't where the problem is, maybe is my view because when I choose the option, the url is correct.</p>