How to check multiple fields for uniqueness?

Question

1C-Bitrix

Described the BookTable entity:

class BookTable extends Entity\DataManager
{
    public static function getMap()
    {
        return array(
            new Entity\IntegerField('ID'),
            new Entity\StringField('ISBN'),
            new Entity\StringField('TITLE'),
        );
    }
}

How to call BookTable::update()instead BookTable::add()if one of the rows of the table already has the added values ​​of the ISBN and TITLE fields (that is, this pair is not unique)?

Answer 1

You do getList, with the filter on ISBN and TITLE.
Further condition, if the record is update, if not add