Db::getInstance PHP Method

    public static function getInstance($config = null)
    {
        if (!self::$_instance instanceof self) {
            self::$_instance = new self($config);
        }
        return self::$_instance;
    }

    public function init()
    {
        if (Tools::getValue('supplier_rewrite')) {
            $name_supplier = str_replace('-', '%', Tools::getValue('supplier_rewrite'));
            //
            // TODO:: need to core update Prestashop code and
            // DB for link_rewrite for suppliers
            // Should we use the Mysql FullText Index Search ??
            //
            $sql = 'SELECT sp.`id_supplier`
				FROM `' . _DB_PREFIX_ . 'supplier` sp
				LEFT JOIN `' . _DB_PREFIX_ . 'supplier_shop` s ON (sp.`id_supplier` = s.`id_supplier`)
				WHERE sp.`name` LIKE \'' . $name_supplier . '\'';
            if (Shop::isFeatureActive() && Shop::getContext() == Shop::CONTEXT_SHOP) {
                $sql .= ' AND s.`id_shop` = ' . (int) Shop::getContextShopID();
            }
            $id_supplier = Db::getInstance(_PS_USE_SQL_SLAVE_)->getValue($sql);
            if ($id_supplier > 0) {
                $_GET['id_supplier'] = $id_supplier;
            } else {
                //TODO: Do we need to send 404?
                header('HTTP/1.1 404 Not Found');
                header('Status: 404 Not Found');
            }
        }
        parent::init();
    }