可用方法
$user ->roles ()->save ()
$user ->roles ()->savemany ()
save 和savemany 接收模型实例
$user ->roles ()->create()
$user ->roles ()->createmany()
接收数组，分别一维数组和二维数组
attach ()接收id 或者数组
detach ()接收id 或者数组
sync ()接收数组
toggle ()接收数组
更新belongto 关联
->associate($account)更新外键
取消dissociate($account)
更新父级时间戳
protected $touches = ['post'];
