Instant MySQL Update from a PHP Page - AJAX? - php

Question

Had a search, but nothing really suggests a good route for me (might be my bad).
I've built a system to be run on an iPad - and to work as a counter for people entering a venue. Essentially, it's a simple insert into a MySQL database from PHP of a record each time a button is pressed on a web page.
That is, when someone enters the venue, a person on the door presses "In" when someone leaves "Out", an 'in time' is inserted into a MySQL database, and an 'out time' so at any time we can find out how many people were in the venue.
Simples. However, of course, it's quite slow, when multiple people are entering the venue at any one time, so I was wondering how you guys would deal with this. I've looked at AJAX, and I must admit this isn't really my field, but I've had a play. I'm naturally concerned about not losing any data, but also, we can't have the system waiting for 10 secs to reload the page.
My original idea was to have an AJAX 'thing' - which when the 'IN'/'OUT' button is pressed, it calls another PHP page to do the MySQL insert. Is this sensible? Or is there a better way of doing this? As my concern with the AJAX solution is that a new call of that 'insert.php' page, would cancel execution of a previous one, so data may get lost? Am I right?
Any insights anyone has would be VERY helpful.
Thanks in advance.
Ryan

Answer 1

You can achieve this easily using jquery.
First post data from main file and catch data in another file using $_POST['message'], to acknowledge data saved successfully you can output json. Here is example
On your html or php page
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.5/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$("#send_data").click(function(event){
var message= 'This is my message';
sendtodb(message);
});
});
function sendtodb(message){
$.post("save.php",{message:message},function(data){
alert(data.status);
},"json");
}
</script>
Now on secon file where you will save data:
<?php
$msg=$_POST['message'];
mysql_query("insert query");
json_encode(array('status'=>'data saved'));
?>

Answer 2

You'd probably be better to have more than one button on the layout, something like:
IN: 1 2 3 4 5 6 7 8 9 10
OUT: 1 2 3 4 5 6 7 8 9 10
It'd save on the number of requests being sent (and the need to press the same button 10 times).
Other than that, Ajax might be an idea, but you'd need some output to the user so that they know their press of the button has actually done something (as it's not refreshing the page, it's not obvious its doing anything).
But if it's taking that long to reload the page, then the bottleneck might not be because the page is reloading - it could be that the server is getting overloaded with requests (which doing my suggestion above should reduce), or could be the result of some badly written code taking a while to execute.

Answer 3

I think using AJAX is the way forward here, and jQuery does indeed make it really easy. Just a few extra thoughts and ideas:
Potentially a race condition could occur if a user keeps clicking before the ajax request has actually completed, particularly if the server becomes overloaded. I would do what Google search does here, and make sure you keep a record of the previous AJAX request and cancel it when a new one is launched, see this other post
With your back end PHP script, I reckon it's quite likely that this will form part of a larger PHP application. Try to make sure that any other processing that might be done for the front end site, such as building menus for example, isn't done on an AJAX request, because you don't need it and it just wastes processor time.
For more robustness, send a return value from your PHP script which maybe includes a status code, so you can detect if the call actually completed.