How to change the price when adding/changing an element of the trade catalog?

Question

1C-Bitrix

You need to generate a price based on the purchase price.

To do this, I decided to use the "OnProductAdd" event and this is what happened:

reveal the code

function ProductAddPriceHandler($id, $arFields)
{
    $purchasePrice = $arFields['PURCHASING_PRICE'];
    $id = $arFields['ID'];

    if ($purchasePrice <= 100) {
        $productPrice = ($purchasePrice / 100 * 100) + $purchasePrice;
    } elseif ($purchasePrice >= 101 and $purchasePrice <= 500) {
        $productPrice = ($purchasePrice / 100 * 75) + $purchasePrice;
    } elseif ($purchasePrice >= 501 and $purchasePrice <= 1000) {
        $productPrice = ($purchasePrice / 100 * 60) + $purchasePrice;
    } elseif ($purchasePrice >= 1001 and $purchasePrice <= 2000) {
        $productPrice = ($purchasePrice / 100 * 50) + $purchasePrice;
    } elseif ($purchasePrice >= 2001 and $purchasePrice <= 4000) {
        $productPrice = ($purchasePrice / 100 * 40) + $purchasePrice;
    } elseif ($purchasePrice >= 4001) {
        $productPrice = ($purchasePrice / 100 * 30) + $purchasePrice;
    }

    $arProductPriceFields = array(
        'PRODUCT_ID' => $id,
        'CATALOG_GROUP_ID' => 1,
        'PRICE' => 500,
        'CURRENCY' => 'RUB',
    );

    $result = \Bitrix\Catalog\Model\Price::add($arProductPriceFields);
}

The event fires, but the price is not added.

Googled, it turns out there is a similar bug from 2012. I did not try the solution from there, because I did not understand how to implement it.

Question: what's wrong? And is the bug relevant, who faced it?

Answer 1

Your main mistake is that you just want to add a price, but the product may already have it. Therefore, you first need to get the item's price id. If not, then add, otherwise update.
If you look in the documentation, then there is a good example

$res = CPrice::GetList(
        array(),
        array(
                "PRODUCT_ID" => $PRODUCT_ID,
                "CATALOG_GROUP_ID" => $PRICE_TYPE_ID
            )
    );

if ($arr = $res->Fetch())
{
    CPrice::Update($arr["ID"], $arFields); //если есть обновляем
}
else
{ //иначе добавляем
    CPrice::Add($arFields);
}