老师我想实现一个类似京东的多功能筛选

如果选3项 则url是这样 show/filter?pid=1&cid=2&yid=3
如果选2项 则url是这样 show/filter?pid=1&yid=2
如果选1项 则url是这样 show/filter?yid=1

于是写出下面的代码。。但实际情况却是 无论怎么点。。都只是 选择一项的筛选链接。。
怎么怎么办呢

@show.router('/filter')
def filter_by():
     pingpai = [
          {'id'=1, 'title':'品牌1'}, 
          {'id':2, title='品牌2'}, 
          {'id':3, title='品牌3'}
     ]

     caizi = [
          {'id':1, title='材质1'},
          {'id':2, title='材质2'},
          {'id':3, title='材质3'}
     ]

     yongtu = [
          {'id':1, title='用途1'},
          {'id':2, title='用途2'},
          {'id':3, title='用途3'}
     ]

     return render_template('/show/filter.html', pingpai=pingpai, caizi=caizi, yongtu=yongtu)




<div class="row">
 <div class="fn">品牌：</div>
     <div class='fn-list'>
     {% for p in pingpai %}
     <a href="{{ url_for('shop.filter_by', pid=p.id) }}">{{ p.title }}</a> 
     {% endfor %}
     </div>
</div>
<div class="row">
     <div class="fn">材质：</div>
     <div class='fn-list'>
     {% for c in caizi %}
     <a href="{{ url_for('shop.filter_by', cid=c.id) }}">{{ c.title }}</a> 
     {% endfor %}
     </div>
</div>
<div class="row">
     <div class="fn">用途：</div>
     <div class='fn-list'>
     {% for y in yongtu %}
     <a href="{{ url_for('shop.filter_by', yid=y.id) }}">{{ y.title }}</a> 
     {% endfor %}
     </div>
</div>