https://medium.com/%E5%BE%9E%E9%9B%B6%E9%96%8B%E5%A7%8B%E7%9A%84%E6%94%BB%E5%9F%8E%E7%8D%85%E7%94%9F%E6%B4%BB/laravel-eloquent-%E8%B3%87%E6%96%99%E8%A1%A8%E9%97%9C%E8%81%AF-relationship-%E6%87%89%E7%94%A8%E6%8C%87%E5%8D%97-1-%E9%9B%99%E8%B3%87%E6%96%99%E8%A1%A8%E9%97%9C%E8%81%AF-777f2c909759