在浏览器上更新数据库关闭

Question

I have a website I'm creating and I want to be able to see who is online and who is not. Seeing who is online is not hard, when you log in, "online" field in database changes from 0 to 1. But the problem is with going offline. I managed to do that IF the person logs out on the log out button and gets redirected to logout.php page:

<?php
session_start();
$user_check=$_SESSION['login_user'];

if(session_destroy())
{
$connection = mysql_connect("localhost", "root", "");
$db = mysql_select_db("masterrad", $connection);

$query2 = mysql_query("update users set online = '0' where username = '$user_check'", $connection);

header("Location: index.php");
}
?>

But if he just closes the page nothing will change in the database since he never went to the logout.php page.

So I was wondering if there is a better way to do this?

Answer 1

On each page that you consider to be an 'online' page.
You could use @Alec Deitloffs idea of a 'last_time_spotted' field and update the online flag based on that and your time period. No cron needed.

$query2 = mysql_query("update users set `online` = '0' where `online` = '1' AND (`last_time_spotted` < NOW() - INTERVAL 15 MINUTE), $connection);

Answer 2

The way that most sites perform this, I believe, is by having a "last time spotted" field in the database. Every time the user goes to a new page, that field is updated for them to the current time. A cron job would execute every 10, 15 minutes (whatever you want), and if the current time minus the time the user was last spotted is greater than the threshold you want (ie, inactive for seven minutes), then you would consider them offline.

It's very, very difficult to actually have code execute completely and successfully when a user leaves the page, closes the browser, et cetera. Unfortunately, this means that alternative methods need to be taken, and it's my understanding that this is the most popular choice. Or at least, one of the simpler ones to implement.