app\models\UserAccount::setUserId PHP Method

    public function setUserId($userId)
    {
        if (self::hasUserId($userId)) {
            return;
        }
        for ($i = 1; $i <= 5; $i++) {
            $field = "user_id{$i}";
            if (!$this->{$field}) {
                $this->{$field} = $userId;
                break;
            }
        }
    }