Why doesn't CCatalogProduct::Update work when adding a new item?

Question

CMS

Good afternoon!
There is a task: when adding a new product to Bitrix, automatically put down its quantity.
My code:

AddEventHandler("iblock", "OnAfterIBlockElementAdd", Array("UpdateClass", "OnAfterIBlockElementAddHandler"));
class UpdateClass
{
    
    function OnAfterIBlockElementAddHandler(&$arFields)
    {
        
          $PRODUCT_ID = $arFields['ID'];
                    $arFields = array('ID' => $arFields['ID'], 'QUANTITY' => 1);// количество товара
                    CCatalogProduct::Update($PRODUCT_ID, $arFields);
    }
}

But the item quantity is not updated. I started to figure out what was the matter, and eventually found out that updating the fields does not work for the newly created element. If you put the ID of another element in PRODUCT_ID, everything works fine.
What could be the reason?

Answer 1

You confuse adding a new product and a new infoblock element. These are two different tables and different modules.
For the "when adding a product" event, you need an OnProductAdd
handler And here see other possible events of the "shopping catalog" module