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Fatal error: Call to a member function query() on a non-object
مربوط به این کد هست


public function Read($id) {

        //$db = database::getInstance();

        $sql = "SELECT * FROM sessions WHERE id = '$id' ";

        //$params = array(':id' => $id);

        //$query = 'SELECT * FROM `sessions` WHERE (`id`=\'' . mysql_real_escape_string($id) . '\')';

        try {

            $db->query($sql);    

            //$result = mysql_query($query);

        } catch(Exception $e) {

            return '';

        }

        /**if (mysql_num_rows($result) != 1) {

        *    return '';

        **}

        **/

        $count = $db->getCountRows();

        if($count == 0){

            //return '';

            var_dump($count);

            echo $sql;

        } 

        //$data = mysql_fetch_assoc($result);

        $data = $db->loadResult();

        $time = strtotime($data['modified']);

        $hash = $data['hash'];

        if (time() - $time > $this -> time_out || strcasecmp($this -> browser_hash, $hash) != 0) {

            return '';

        }

        return $data['data'];

    }