How to get errors in yii model

public static function getModelError($model) {

    $errors = $model->getErrors();    //得到所有的错误信息

    if(!is_array($errors)) return '';

    $firstError = array_shift($errors);

    if(!is_array($firstError)) return '';

    return array_shift($firstError);

}

$model = new User();

$model->name = $name;

$model->nick_name = $nick_name;

$model->phone = $phone;

$model->sex = $sex;

$model->isNewRecord = true;      //此语句可省略

if(!$model->save()){         //保存不成功

throw new \RuntimeException('保存败.'.$model::getModelError($model));

}