public static function boot()
{
parent::boot();
static::saved(function ($classes) {
self::$lastClassesId = $classes->classes_id;
});
// 將導師的班級資料設定為0，刪除排課設定
static::deleting(function ($classes) {
$teacher = Teacher::where('classes_id', '=', $classes->classes_id)->update(array('classes_id' => 0));
$courseUnit = Courseunit::where('classes_id', '=', $classes->classes_id)->delete();
});
}