https://blog.wongcw.com/2020/06/26/hw-3-0%e7%89%88model-3%e6%8b%86%e8%a7%a3%e7%89%b9%e6%96%af%e6%8b%89%e7%9a%84%e9%bb%91%e7%a7%91%e6%8a%80%e7%b5%82%e6%ad%b8%e4%b9%9f%e5%be%97%e5%90%91%e6%88%90%e6%9c%ac%e4%bd%8e%e9%a0%ad/