laravel DB事物

public function store(Request $request, $id)
{
    $externalAccount = ExternalAccounts::find($id);
    DB::beginTransaction();
    try {
        $externalAccount->fund_number = 999;
        $externalAccount->capital_balance = 'kjhkjhkj';
        $externalAccount->save();
        DB::commit();
    } catch (Exception $e){
       DB::rollback();
       throw $e;
    }
}