OpenCart DB CACHED db driver - mysql, mysqli etc

<?php
// changed by Doru Brad
// email me at dorubrad@gmail.com
// this will cache queries using the opencart cache
// just replace your db.php file with this one under system->library
class DB {
    private $driver;
    private $cache;
    private $cachedquery;

    public function __construct($driver, $hostname, $username, $password, $database) {
        $this->cache = new Cache(DB_CACHED_EXPIRE);

        $file = DIR_DATABASE . $driver . '.php';

        if (file_exists($file)) {
            require_once($file);

            $class = 'DB' . $driver;

            $this->driver = new $class($hostname, $username, $password, $database);
        } else {
            exit('Error: Could not load database driver type ' . $driver . '!');
        }
    }

    public function query($sql) {
        $md5query = md5($sql);

        if ($query = $this->cache->get('sql_' . $md5query))
        {
            if ($query->sql == $sql)
            {

                if ($resetflag = $this->cache->get('sql_globalresetcache'))
                {
                    if ($resetflag <= $query->time)
                    {
                        $this->cachedquery = $query;
                        return $query->return;
                    };
                }
                else
                {
                    $this->cachedquery = $query;
                    return $query->return;
                };

            }
        }

        $return = $this->driver->query($sql);

        $query = new stdClass();
        $query->return = $return;
        $query->sql = $sql;
        $query->time = time();

        unset($this->cachedquery);

        $this->cache->set('sql_' . $md5query, $query);
        return $return;
    }

    public function escape($value) {
        return $this->driver->escape($value);
    }

    public function countAffected() {
        return $this->driver->countAffected();
    }

    public function getLastId() {
        return $this->driver->getLastId();
    }
}
?>