http://www.w3schools.com/Ajax/ajax_database.asp
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 customer in the drop-down box below:
Select a Customer: Alfreds Futterkiste North/South Wolski Zajazd
CustomerID
ALFKI
CompanyName
Alfreds Futterkiste
ContactName
Maria Anders
Address
Obere Str. 57
City
Berlin
PostalCode
12209
Country
Germany
AJAX example explained
The example above contains a simple HTML form and a link to a JavaScript:
<html>
<head>
<script type="text/javascript" src="selectcustomer.js"></script>
</head>
<body>
<form>
Select a Customer:
<select name="customers" onchange="showCustomer(this.value)">
<option value="ALFKI">Alfreds Futterkiste</option>
<option value="NORTS ">North/South</option>
<option value="WOLZA">Wolski Zajazd</option>
</select>
</form>
<div id="txtHint"><b>Customer 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 "showCustomer()" 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 showCustomer() is called.
The AJAX JavaScript
This is the JavaScript code stored in the file "selectcustomer.js":
var xmlhttp
function showCustomer(str)
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
{
alert ("Your browser does not support AJAX!");
return;
}
var url="getcustomer.asp";
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 AJAX server page
The server page called by the JavaScript above, is an ASP file called "getcustomer.asp".
The ASP page is written in VBScript for an Internet Information Server (IIS). It could easily be rewritten in PHP, or some other server language. Look at a corresponding example in PHP.
The code runs a query against a database, and returns the result in an HTML table:
<%
response.expires=-1
sql="SELECT * FROM CUSTOMERS WHERE CUSTOMERID="
sql=sql & "'" & request.querystring("q") & "'"
set conn=Server.CreateObject("ADODB.Connection")
conn.Provider="Microsoft.Jet.OLEDB.4.0"
conn.Open(Server.Mappath("/db/northwind.mdb"))
set rs=Server.CreateObject("ADODB.recordset")
rs.Open sql,conn
response.write("<table>")
do until rs.EOF
for each x in rs.Fields
response.write("<tr><td><b>" & x.name & "</b></td>")
response.write("<td>" & x.value & "</td></tr>")
next
rs.MoveNext
loop
response.write("</table>")
%>
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