How to set the quantity of goods automatically in Bitrix when adding?

Question

CMS

Good afternoon!
Website edited by Small Business. There is a task - when adding a product to the Bitrix catalog, you need to automatically register the article, and the quantity of the product should automatically be scored equal to 1. I figured out the article, the code is given below.

AddEventHandler("iblock", "OnBeforeIBlockElementAdd", Array("ArtClass", "OnBeforeIBlockElementAddHandler"));

class ArtClass
{
    function OnBeforeIBlockElementAddHandler(&$arFields)
    {
    $arSort= Array();
    $arFilter = Array("IBLOCK_ID"=>4, "ID"=>$arFields['ID']);
    $arSelect = Array();
    $res =  CIBlockElement::GetList($arSort, $arFilter, false, false, $arSelect);
    $res2 = $res->Fetch();
        
                if($arFields['IBLOCK_ID'] == 4)
        {
          $arFields['PROPERTY_VALUES'][306] = $res2["ID"];
        }      
    }
}

And with the amount of goods there was a plug. How to do the same for the quantity on the Internet did not find suitable information. Please tell me how can this be done.

Answer 1

CCatalogProduct ::Update
https://dev.1c-bitrix.ru/api_help/catalog/classes/...
after the element itself has been created.