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

   @app.route('/comment/',methods=['POST'])
   @loginFirst
   def comment():
       comment=request.form.get('new_comment')
       ques_id=request.form.get('question_id')
       auth_id=User.query.filter(User.username==session.get('user')).first().id
       comm=Comment(author_id=auth_id,question_id=ques_id,detail=comment)
       db.session.add(comm)
       db.session.commit()
       return redirect(url_for('questiondetail',question_id=ques_id))

    

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

   {% extends'base.html' %}
   
   {% block title %}
       问答详情
   {% endblock %}
   
   {% block head %}
       <link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='css/questiondetail.css') }}">
   {% endblock %}
   
   {% block main %}
       <div class="post">
       <div class="artical">
           <h1 style="text-align: center">{{ ques.title }}</h1>
           <br><small>用户：{{ ques.author.username }} <span class="badge">{{ ques.create_time }}</span></small>
           <hr>
           <p class="lead">{{ ques.detail }}</p>
       </div>
           <form action="{{ url_for('comment') }}" method="post" style="align-content: inherit">
               <div class="sign-container">
                       <textarea class="form-control" rows="8" id="QuestionDetail" name="new_comment"></textarea>
                       <input name="question_id" type="hidden" value="{{ ques.id }}"/>
                   <br>
                   <input type="submit" value="评论" style="float: right">
                   <h4>评论({{ ques.comments|length }})</h4>
                   <hr>
               </div>
           </form>
           <ul class="list-group" style="background-size: contain">
               {% for foo in ques.comments %}
               <li>
                   <span class="glyphicon glyphicon-leaf" aria-hidden="true"></span>
                   用户：<a href="#" target="_blank">{{ foo.author.username }}</a>
                   <span class="badge">{{ foo.creat_time }}</span>
                   <br>
                   <p style="text-indent: 18px">{{ foo.detail }}</p>
               </li>
               {% endfor %}
       </ul>
       </div>
   {% endblock %}