AJAX can be used for interactive communication with a database.

AJAX database example

The following example will demonstrate how a web page can fetch information from a database with AJAX technology.

Select a person:

Person info will be listed here.

Example explained – The MySQL Database

The database table we use 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

Example explained – The HTML page

The HTML page contains a link to an external JavaScript, an HTML form, and a div element:

<html>
<head>
<script type="text/javascript" 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>
<br />
<div id="txtHint"><b>Person info will be listed here.</b></div>

</body>
</html>

As you can see it is just a simple HTML form with a drop down box called "customers".

The <div> below the form will be 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 change the value in the drop down box, the function showUser() is called.

Example explained – The JavaScript code

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)
{
document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
}
}

function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
{
// code for IE7+, Firefox, Chrome, Opera, Safari
return new XMLHttpRequest();
}
if (window.ActiveXObject)
{
// code for IE6, IE5
return new ActiveXObject("Microsoft.XMLHTTP");
}
return null;
}

The stateChanged() and GetXmlHttpObject functions are the same as in the PHP AJAX Suggest chapter, you can go to there for an explanation of those.

The showUser() Function

When a person in the drop-down box is selected, the showUser() function executes the following:

  1. Calls the GetXmlHttpObject() function to create an XMLHTTP object
  2. Defines an URL (filename) to send to the server
  3. Adds a parameter (q) to the URL with the content of the drop-down box
  4. Adds a random number to prevent the server from using a cached file
  5. Each time the readyState property changes, the stateChanged() function will be executed
  6. Opens the XMLHTTP object with the given URL
  7. Sends an HTTP request to the server

Example explained – The PHP Page

The PHP page called by the JavaScript, is called "getuser.php".

The PHP script runs an SQL query against a MySQL database, and returns the result as HTML:

<?php
$q=$_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 "<table border=’1′>
<tr>
<th>Firstname</th>
<th>Lastname</th>
<th>Age</th>
<th>Hometown</th>
<th>Job</th>
</tr>";

while($row = mysql_fetch_array($result))
{
echo "<tr>";
echo "<td>" . $row['FirstName'] . "</td>";
echo "<td>" . $row['LastName'] . "</td>";
echo "<td>" . $row['Age'] . "</td>";
echo "<td>" . $row['Hometown'] . "</td>";
echo "<td>" . $row['Job'] . "</td>";
echo "</tr>";
}
echo "</table>";

mysql_close($con);
?>

When the query is sent from the JavaScript to the PHP page, the following happens:

  1. PHP opens a connection to a MySQL server
  2. The correct person is found
  3. An HTML table is created, and filled with data, and sent back to the "txtHint" placeholder