完成评论功能

1. 定义评论的视图函数
   @app.route('/comment/',methods=['POST'])
   def comment()：
   读取前端页面数据，保存到数据库中
2. 用<input type="hidden" 方法获取前端的"question_id" 
3. 显示评论次数
4. 要求评论前登录
5. 尝试实现详情页面下的评论列表显示

   # 跳转发布详情
   @app.route('/fabuview/<fabu_id>')  # 和idea的update一样，将id带到控制器
   def fabuview(fabu_id):
       fa = Fabu.query.filter(Fabu.id == fabu_id).first()  # 根据id查询出整条元组记录，丢进fa
       comments = Comment.query.filter(Comment.fabu_id==fabu_id).all()
       return render_template('fabuview.html', fa=fa,comments=comments)  # 把值fa丢进键fa，在fabuview.html页面调用
   
   
   # 方法二：
   # fabu={
   # 'fa':Fabu.query.filter(Fabu.id == fabu_id).first()
   # }
   # return render_template('fabuview.html',**fabu)
   
   
   @app.route('/comment/',methods=['POST'])
   @loginFirst
   def comment():
       detail = request.form.get('pinglun')
       author_id = User.query.filter(User.username == session.get('user')).first().id
       fabu_id = request.form.get('fa_id')
       comment = Comment(detail=detail,author_id=author_id,fabu_id=fabu_id)
       db.session.add(comment)  # 执行操作
       db.session.commit()  # 提交到数据库
       return redirect(url_for('fabuview',fabu_id=fabu_id))

   {% extends 'daohang.html' %}
   {% block fabu_viewtitle %}发布内容{% endblock %}
   {% block fabu_viewhead %}
       <link rel="stylesheet" href="http://cdn.static.runoob.com/libs/bootstrap/3.3.7/css/bootstrap.min.css">
       <script src="http://cdn.static.runoob.com/libs/jquery/2.1.1/jquery.min.js"></script>
       <script src="http://cdn.static.runoob.com/libs/bootstrap/3.3.7/js/bootstrap.min.js"></script>
   {% endblock %}
   {% block daohangbody %}
       <div class="col-md-2 column "></div>
       <div class="col-md-8 column ">
           <h2 href="#" class="text-center">{{ fa.title }}</h2>
           <br>
           <p class="text-center">
               <a href="#">
                   <small>{{ fa.author.username }}</small>
               </a>&nbsp&nbsp&nbsp
               <span class="pull-center"><small>{{ fa.creat_time }}</small></span>
           </p>
           <hr>
           <p>{{ fa.detail }}</p>
           <hr>
   
           <form action="{{ url_for('comment') }}" method="post">
               <div class="form-group">
                       <textarea name="pinglun" class="form-control" rows="5" id="pinglun"
                                 placeholder="请输入评论"></textarea>
                   <input type="hidden" name="fa_id" value="{{ fa.id }}">
               </div>
               <button type="submit" class="btn btn-default">发送</button>
               <br>
               <br>
               <h4>评论：（{{ fa.comments|length }}）</h4>
               <ul class="list-unstyled">
                   {% for foo in comments %}
                       <li class="list-group-item">
                           <a>{{ foo.author.username }}</a>
                           <span class="badge pull-right">{{ foo.creat_time }}</span>
                           <p>{{ foo.detail }}</p>
                           <br>
                       </li>
                   {% endfor %}
               </ul>
           </form>
           <br>
           <br>
           <br>
   
       </div>
       <div class="col-md-2 column "></div>
   {% endblock %}