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

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

   　　

   <form role="form" action="{{ url_for('comment') }}" method="post">
                   <div class="form-group">
                       <label for="exampleInputEmail1">Write down your answer~~</label>
                       <textarea class="form-control" id="exampleInputEmail1" name="new_comment"></textarea>
                       <input type="hidden" name="question_id" value="{{ quest.id }}">
                   </div>
                   <button type="submit" class="btn btn-default">Submit</button>
               </form>
   

   　　

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

2. # 装饰器
   def loginFrist(func):
       @wraps(func)
       def wrapper(*args, **kwargs):
           if session.get('user'):
               return func(*args, **kwargs)
           else:
               return redirect(url_for('login'))
       return wrapper