完成評論功能

1. 定義評論的視圖函數
   @app.route('/comment/',methods=['POST'])
   def comment()：
   讀取前端頁面數據，保存到數據庫中

   @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" 方法獲取前端的"question_id" 

    <input type="hidden" name="question_id" value="{{ ques.id }}">

3. 顯示評論次數

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

4. 要求評論前登陸

   @loginFirst

5. 嘗試實現詳情頁面下的評論列表顯示