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Implementing AJAX with PHP and MySQL

Saturday, June 17th, 2006

I thought I would post about the recent AJAX addition to my site, that active search. AJAX is not a technology, it is a methodology of making programmatic callbacks from javascript functioning, using XML and HTML. How it works is an event is set for a textbox, textarea, body event, button click, etc. Within this event there is a callback to another javascript function that loads, processes, or does whatever necessary to the page that is called, and returns the results via javascript. In my case, I completed my first script as follows:

The form action is contained as follows:
<form action="search.php" method="get">

The textbox is defined as follows:
< label for="query">
< input type="text" style="text-align: center;" name="search" autocomplete="off" id="query" onKeyUp="preSearch()" />
< /label>

Now comes the fun part, the javascript function preSearch is defined as follows:
< script language="javascript">
var xmlhttp = false;

if (window.XMLHttpRequest) {
xmlhttp = new XMLHttpRequest();
} else if (window.ActiveXObject) {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

function preSearch() {
var theQuery = document.getElementById('query').value ;

if(theQuery !== "") {
document.getElementById('result').innerHTML = "Searching...";
var url = 'search.php?q=' + theQuery;'GET', url, true);
xmlhttp.onreadystatechange = function() {
if(xmlhttp.readyState == 4 && xmlhttp.status == 200) {
document.getElementById('result').innerHTML = xmlhttp.responseText + ' ';
} else {
//document.getElementById('result').innerHTML = 'Error: preSearch Failed!';
< /script>

After you have implementing all of the above properly, the only other part you have to complete is your php or html page that will print the results, in this cause I have called it to search.php, which contains the following code:

< ?

if (empty($q)) {
Header("Location: index.php");
} else {
$connection->doQuery("SELECT * FROM news WHERE news LIKE '%$q%' LIMIT 10");
$results = $connection->getAllData();

if (!empty($results)) {
$count = 1;
foreach ($results as $result) {
< ?=$count?>) < a href="?mod=news&id=<?=$result["id"]?>">< ?=substr($result["news"], 0, 17)?>...< /a>< br />
< ?
< br />
< ?
} else {
< center>< b>No results found.< /b>< /center>
< br />
< ?

While AJAX is a very cool aspect to add to your webpage, there are implications. The constant callbacks to pages that are searching content from an AJAX-enabled page do add a large amount of traffic for the server to handle. This is why you don't see alot of larger sites using AJAX (Yet). There is research in progress to solve this problem using Caching as well as some other pretty cool technologies. Another issue is security, I won't get too in-depth into this right now because looking at my code above I can already think of a few ways to exploit the code to gain un-wanted access on some content of my website.

That's my speal on AJAX for now, I am also currently playing with AJAX.NET which will alow for the use of AJAX within ASP.NET pages written in VB.NET and C#. More to come soon. Let me know if you think there are ways to improve what I have written above. Cheers.


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