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('detail' , question_id = ques_id))

2. 用<input type="hidden" 方法获取前端的"question_id" 

   <form action="{{ url_for('comment') }}" method="post" style="margin: 20px">
           <div class="form-group">
               <textarea name="new_comment" class="form-control" rows="3" id="new-comment" placeholder="write your comment"></textarea>
               <input type="hidden" name="question_id" value="{{ ques.id }}">
           </div>
           <button type="submit" class="btn btn-default">发送</button>
       </form>

3. 显示评论次数

   <h4>评论:({{ ques.comments|length }})</h4>

4. 要求评论前登录

   @app.route('/comment/',methods=['POST'])
   @loginFirst

5. 尝试实现详情页面下的评论列表显示