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AJAX Database

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AJAX can be used for interactive communication with a database.

AJAX Database Example

In the AJAX example below we will show how a web page can fetch information from a MySQL database using AJAX technology.

User info will be listed here.

This example consists of four elements:

a MySQL database
a simple HTML form
a JavaScript
a PHP page
The Database
The database we will be using in this example looks like this:

id	FirstName	LastName	Age	Hometown	Job
1	Peter	Griffin	41	Quahog	Brewery
2	Lois	Griffin	40	Newport	PianoTeacher
3	Joseph	Swanson	39	Quahog	PoliceOfficer
4	Glenn	Quagmire	41	Quahog	Pilot

The HTML Form

The example above contains a simple HTML form and a link to a JavaScript:

<html><head>
<script src="selectuser.js"></script>
</head>
<body>
<form>
Select a User:
<select name="users" onchange="showUser(this.value)">
<option value="1">Peter Griffin</option>
<option value="2">Lois Griffin</option>
<option value="3">Glenn Quagmire</option>
<option value="4">Joseph Swanson</option>
</select>
</form>
<p>
<div id="txtHint"><b>User info will be listed here.</b></div>
</p>
</body></html>

Example Explained - The HTML Form

As you can see it is just a simple HTML form with a drop down box called "users" with names and the "id" from the database as option values.

The paragraph below the form contains a div called "txtHint". The div is used as a placeholder for info retrieved from the web server.

When the user selects data, a function called "showUser()" is executed. The execution of the function is triggered by the "onchange" event.

In other words: Each time the user changes the value in the drop down box, the function showUser() is called.

The JavaScript

This is the JavaScript code stored in the file "selectuser.js":

var xmlHttp
function showUser(str)
{
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
{
alert ("Browser does not support HTTP Request")
return
}
var url="getuser.php"
url=url+"?q="+str
url=url+"&sid="+Math.random()
xmlHttp.onreadystatechange=stateChanged
xmlHttp.open("GET",url,true)
xmlHttp.send(null)
}
function stateChanged()
{
if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
{
document.getElementById("txtHint").innerHTML=xmlHttp.responseText
}
}
function GetXmlHttpObject()
{
var xmlHttp=null;
try
{
// Firefox, Opera 8.0+, Safari
xmlHttp=new XMLHttpRequest();
}
catch (e)
{
//Internet Explorer
try
{
xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}