function setTimeZone($timeZone){
		if($this->currentTimeZone == $timeZone){
			// $timeZone is set already 
			return;
		}
		$this->currentTimeZone = $timeZone;
		
		//convert php timezone into mysql timezone format
    	$dtz = new \DateTimeZone($timeZone);
    	$timeInTimeZone = new \DateTime('now', $dtz);
    	
    	$sign = "+";
    	$offset = $dtz->getOffset( $timeInTimeZone ) / 3600;
    	if($offset < 0){
    		$sign = "-";
    		$offset = -1 * $offset;
    	}
    	$hourPart = intval($offset);
    	$minutePart = $offset-$hourPart;
    	$minutePart = $minutePart * 60;
    	
    	$timeZoneForMySql = $sign.$hourPart.":".$minutePart;
    	
    	// set the timezone in mysql
    	$this->query("SET time_zone='$timeZoneForMySql'");
    }