private function checkValidity()
    {

        if (!is_writable($this->rssFile)) {
            $this->valid = false;
            return;
        }

        $stmt = $this->db->prepare('SELECT CREATED FROM ' . $this->table . ' ORDER BY CREATED DESC LIMIT 1');
        $stmt->execute();
        $res = $stmt->fetchAll();

        if (count($res) == 0) {
            $this->valid = false;
            return;
        }

        $latestInput = strtotime($res[0]->CREATED);

        $rssCreated = filemtime($this->rssFile);

        if ($latestInput > $rssCreated) {
            $this->valid = false;
        } else {
            $this->valid = true;
        }
    }