Only get new data from PHP file - jQuery - php

Question

Instead of reloading old data from a PHP file that I parse with JavaScript using JSON, I want to ONLY load new data. My project is a little multiplayer environment and my goal is to have all users see either other move in realtime.
Here is my code:
JavaScript:
function getUsers() {
$.get("database/getData.php", function(data) {
// data returned from server;
for(var i = 0; i < data.response.length; i++) {
// users obtained from the array... parse them now
var user = data.response[i].split(" ");
// user info
var id = user[0];
var username = user[1];
var xx = user[2];
var yy = user[3];
userCount = data.response.length;
$(".online").html(userCount + " users online right now.")
// position the users
moveCharacter(username, xx, yy);
}
}, "json");
}
var infoGetter = setInterval(getUsers, 2000); // we may need to improve this... type of realtime
And here is my PHP:
<?
$database = sqlite_open("thenew.db", 0999, $error);
if(!$database) die($error);
$query = "SELECT * FROM users";
$results = sqlite_query($database, $query);
if(!$results) die("Canot execute query");
$data = array();
while($row = sqlite_fetch_array($results)) {
$data[] = $row['uid'] . " " . $row['username'] . " " . $row['xPos'] . " " . $row['yPos'];
}
echo json_encode(array("response"=>$data));
sqlite_close($database);
?>
How can I make it so ONLY new data from the PHP file is parsed by the JavaScript instead of all data?
Thanks!

Answer 1

I would suggest you to modify the select query. Instead of having it as select * from users, add some where condition like where userId > somenumber. Now send the last userId which we processed in the last request along with next request which you make from client side. This will make sure that you will always gets new response.

Answer 2

Indeed, with your current setup, every call to "getUsers" will replay the entire state of the game up to the last move made, and not necessarily finish in the correct state. In order to get the behavior you want, you will need to add a timestamp or serial id to the "users" table and then order your results in order to get the most recent moves. You will need to do this for each user separately, so you will also need to provide a mechanism to retrieve and iterate through all users...
Thus your javascript becomes something like...
function getUsers() {
$.get("database/getAllUsers.php", function(data) {
$.each(data, function(i,uid) {
$.get("database/getData.php?uid=".uid, function(data) {
...
and your php query becomes...
$query = "SELECT * FROM users WHERE uid=$_GET['uid'] ORDER BY timestamp DESC LIMIT 1