AJAX Database Example
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AJAX Database Example
In the AJAX example below we will demonstrate how a web page can fetch information from a MySQL
database using AJAX technology.
Select a Name in the Box Below
Select a User:
Peter Griffin
User info will be listed here.
This example consists of four elements:
a
a
a
a
MySQL database
simple HTML form
JavaScript
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="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;
}
Example Explained
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
If an item in the drop down box is selected the function executes the following:
1.
2.
3.
4.
5.
6.
7.
Calls on the GetXmlHttpObject function to create an XMLHTTP object
Defines the url (filename) to send to the server
Adds a parameter (q) to the url with the content of the dropdown box
Adds a random number to prevent the server from using a cached file
Call stateChanged when a change is triggered
Opens the XMLHTTP object with the given url.
Sends an HTTP request to the server
The PHP Page
The server page called by the JavaScript, is a simple PHP file called "getuser.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 HTML table:
<?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);
?>
Example Explained
When the query is sent from the JavaScript to the PHP page the following happens:
1.
2.
3.
PHP opens a connection to a MySQL server
The "user" with the specified name is found
A table is created and the data is inserted and sent to the "txtHint" placeholder
