SORT BY 'date_add' not working on my website

[stefanopsc]

Hello everybody! I am trying to sort the product list from a single manufacturer by date_add, where default is name. I've edited the SQL query in class/manufacturer.php but no matter what it still sorts by name. My code is: 

 

public static function getProducts(
        $idManufacturer,
        $idLang,
        $p,
        $n,
        $orderBy = null,
        $orderWay = null,
        $getTotal = false,
        $active = true,
        $activeCategory = true,
        Context $context = null
    ) {
        if (!$context) {
            $context = Context::getContext();
        }

        $front = true;
        if (!in_array($context->controller->controller_type, array('front', 'modulefront'))) {
            $front = false;
        }

        if ($p < 1) {
            $p = 1;
        }

        if (empty($orderBy) || $orderBy == 'position') {
            $orderBy = 'date_add';
        }

        if (empty($orderWay)) {
            $orderWay = 'DESC';
        }

        if (!Validate::isOrderBy($orderBy) || !Validate::isOrderWay($orderWay)) {
            die(Tools::displayError());
        }

        $groups = FrontController::getCurrentCustomerGroups();
        $sqlGroups = count($groups) ? 'IN ('.implode(',', $groups).')' : '= 1';

        /* Return only the number of products */
        if ($getTotal) {
            $sql = '
				SELECT p.`id_product`
				FROM `'._DB_PREFIX_.'product` p
				'.Shop::addSqlAssociation('product', 'p').'
				WHERE p.id_manufacturer = '.(int) $idManufacturer
                .($active ? ' AND product_shop.`active` = 1' : '').'
				'.($front ? ' AND product_shop.`visibility` IN ("both", "catalog")' : '').'
				AND EXISTS (
					SELECT 1
					FROM `'._DB_PREFIX_.'category_group` cg
					LEFT JOIN `'._DB_PREFIX_.'category_product` cp ON (cp.`id_category` = cg.`id_category`)'.
                    ($activeCategory ? ' INNER JOIN `'._DB_PREFIX_.'category` ca ON cp.`id_category` = ca.`id_category` AND ca.`active` = 1' : '').'
					WHERE p.`id_product` = cp.`id_product` AND cg.`id_group` '.$sqlGroups.'
				)';

            $result = Db::getInstance(_PS_USE_SQL_SLAVE_)->executeS($sql);
            return (int) count($result);
        }
        if (strpos($orderBy, '.') > 0) {
            $orderBy = explode('.', $orderBy);
            $orderBy = pSQL($orderBy[0]).'.`'.pSQL($orderBy[1]).'`';
        }

        if ($orderBy == 'price') {
            $alias = 'product_shop.';
        } elseif ($orderBy == 'name') {
            $alias = 'pl.';
        } elseif ($orderBy == 'manufacturer_name') {
            $orderBy = 'name';
            $alias = 'm.';
        } elseif ($orderBy == 'quantity') {
            $alias = 'stock.';
        } else {
            $alias = 'p.';
        }

        $sql = 'SELECT p.*, product_shop.*, stock.out_of_stock, IFNULL(stock.quantity, 0) as quantity'
            .(Combination::isFeatureActive() ? ', product_attribute_shop.minimal_quantity AS product_attribute_minimal_quantity, IFNULL(product_attribute_shop.`id_product_attribute`,0) id_product_attribute' : '').'
			, pl.`description`, pl.`description_short`, pl.`link_rewrite`, pl.`meta_description`, pl.`meta_keywords`,
			pl.`meta_title`, pl.`name`, pl.`available_now`, pl.`available_later`, image_shop.`id_image` id_image, il.`legend`, m.`name` AS manufacturer_name,
				DATEDIFF(
					product_shop.`date_add`,
					DATE_SUB(
						"'.date('Y-m-d').' 00:00:00",
						INTERVAL '.(Validate::isUnsignedInt(Configuration::get('PS_NB_DAYS_NEW_PRODUCT')) ? Configuration::get('PS_NB_DAYS_NEW_PRODUCT') : 20).' DAY
					)
				) > 0 AS new'
            .' FROM `'._DB_PREFIX_.'product` p
			'.Shop::addSqlAssociation('product', 'p').
            (Combination::isFeatureActive() ? 'LEFT JOIN `'._DB_PREFIX_.'product_attribute_shop` product_attribute_shop
						ON (p.`id_product` = product_attribute_shop.`id_product` AND product_attribute_shop.`default_on` = 1 AND product_attribute_shop.id_shop='.(int)$context->shop->id.')':'').'
			LEFT JOIN `'._DB_PREFIX_.'product_lang` pl
				ON (p.`id_product` = pl.`id_product` AND pl.`id_lang` = '.(int) $idLang.Shop::addSqlRestrictionOnLang('pl').')
				LEFT JOIN `'._DB_PREFIX_.'image_shop` image_shop
					ON (image_shop.`id_product` = p.`id_product` AND image_shop.cover=1 AND image_shop.id_shop='.(int)$context->shop->id.')
			LEFT JOIN `'._DB_PREFIX_.'image_lang` il
				ON (image_shop.`id_image` = il.`id_image` AND il.`id_lang` = '.(int) $idLang.')
			LEFT JOIN `'._DB_PREFIX_.'manufacturer` m
				ON (m.`id_manufacturer` = p.`id_manufacturer`)
			'.Product::sqlStock('p', 0);

        if (Group::isFeatureActive() || $activeCategory) {
            $sql .= 'JOIN `'._DB_PREFIX_.'category_product` cp ON (p.id_product = cp.id_product)';
            if (Group::isFeatureActive()) {
                $sql .= 'JOIN `'._DB_PREFIX_.'category_group` cg ON (cp.`id_category` = cg.`id_category` AND cg.`id_group` '.$sqlGroups.')';
            }
            if ($activeCategory) {
                $sql .= 'JOIN `'._DB_PREFIX_.'category` ca ON cp.`id_category` = ca.`id_category` AND ca.`active` = 1';
            }
        }

        $sql .= '
				WHERE p.`id_manufacturer` = '.(int) $idManufacturer.'
				'.($active ? ' AND product_shop.`active` = 1' : '').'
				'.($front ? ' AND product_shop.`visibility` IN ("both", "catalog")' : '').'
				GROUP BY p.id_product
				ORDER BY '.$alias.'`'.bqSQL($orderBy).'` '.pSQL($orderWay).'
				LIMIT '.(((int) $p - 1) * (int) $n).','.(int) $n;

        $result = Db::getInstance(_PS_USE_SQL_SLAVE_)->executeS($sql);

        if (!$result) {
            return false;
        }

        if ($orderBy == 'price') {
            Tools::orderbyPrice($result, $orderWay);
        }

        return Product::getProductsProperties($idLang, $result);
    }

I can see there is no alias for date_add, but I can't say if this is the problem. Any help would be appreciated! Thank you!