PHP and AJAX responseXML Example

AJAX Database as XML Example

In the AJAX example below we will demonstrate how a web page can fetch information from a MySQL database, convert it to an XML document, and use it to display information in several different places.
This example my seem a lot like the "PHP AJAX Database" example in the last chapter, however there is a big difference: in this example we get the data from the PHP page as XML using the responseXML function.
Receiving the response as an XML document allows us to update this page several places, instead of just receiving a PHP output and displaying it.
In this example we will update several <span> elements with the information we receive from the database.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 Piano Teacher
3 Joseph Swanson 39 Quahog Police Officer
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="responsexml.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>
<h2><span id="firstname"></span>
&nbsp;<span id="lastname"></span></h2>
<span id="job"></span>
<div style="text-align: right">
<span id="age_text"></span>
<span id="age"></span>
<span id="hometown_text"></span>
<span id="hometown"></span>
</div>
</body>
</html>

Example Explained - The HTML Form

  • The HTML form is a drop down box called "users" with names and the "id" from the database as option values.
  • Below the form there are several different <span> elements which are used to as placeholders for the different values we will retrive.
  • 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 and outputs the result in the specified <span> elements.

The JavaScript

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

var xmlHttp;
function showUser(str)
 { 
 xmlHttp=GetXmlHttpObject();
 if (xmlHttp==null)
  {
  alert ("Browser does not support HTTP Request");
  return;
  } 
 var url="responsexml.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")
{
 xmlDoc=xmlHttp.responseXML;
 document.getElementById("firstname").innerHTML=
 xmlDoc.getElementsByTagName("firstname")[0].childNodes[0].nodeValue;
 document.getElementById("lastname").innerHTML=
 xmlDoc.getElementsByTagName("lastname")[0].childNodes[0].nodeValue;
 document.getElementById("job").innerHTML=
 xmlDoc.getElementsByTagName("job")[0].childNodes[0].nodeValue;
 document.getElementById("age_text").innerHTML="Age: ";
 document.getElementById("age").innerHTML=
 xmlDoc.getElementsByTagName("age")[0].childNodes[0].nodeValue;
 document.getElementById("hometown_text").innerHTML="<br/>From: ";
 document.getElementById("hometown").innerHTML=
 xmlDoc.getElementsByTagName("hometown")[0].childNodes[0].nodeValue;
 }
} 
function GetXmlHttpObject()
 { 
 var objXMLHttp=null;
 if (window.XMLHttpRequest)
  {
  objXMLHttp=new XMLHttpRequest();
  }
 else if (window.ActiveXObject)
  {
  objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
 return objXMLHttp;
 }

Example Explained


The stateChanged() Function
If an item in the drop down box is selected the function executes the following:
  1. Defines the "xmlDoc" variable as an xml document using the responseXML function
  2. Retrieves data from the xml documents and places them in the correct <span> elements

The PHP Page

The server page called by the JavaScript, is a simple PHP file called "responsexml.php".
The page is written in PHP and uses a MySQL databse.
The code runs a SQL query against a database and returns the result as an XML document:

<?php
header('Content-Type: text/xml');
header("Cache-Control: no-cache, must-revalidate");
//A date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
$q=$_GET["q"];
$con = mysql_connect('localhost', 'peter', 'abc123');
if (!$con)
 {
 die('Could not connect: ' . mysql_error());
 }
mysql_select_db("ajax_demo", $con);
$sql="SELECT * FROM user WHERE id = ".$q."";
$result = mysql_query($sql);
echo '<?xml version="1.0" encoding="ISO-8859-1"?>
<person>';
while($row = mysql_fetch_array($result))
 {
 echo "<firstname>" . $row['FirstName'] . "</firstname>";
 echo "<lastname>" . $row['LastName'] . "</lastname>";
 echo "<age>" . $row['Age'] . "</age>";
 echo "<hometown>" . $row['Hometown'] . "</hometown>";
 echo "<job>" . $row['Job'] . "</job>";
 }
echo "</person>";
mysql_close($con);
?>

Example Explained

When the query is sent from the JavaScript to the PHP page the following happens:
  1. The content-type of the PHP document is set to be "text/xml"
  2. The PHP document is set to "no-cache" to prevent caching
  3. The $q variable is set to be the data sent from the html page
  4. PHP opens a connection to a MySQL server
  5. The "user" with the specified id is found
  6. The data is outputted as an xml document
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