AJAX can be used for interactive communication with a database.
AJAX Database Example
In the AJAX example below we will demonstrate how a web page can fetch information from a database using AJAX technology.
Select a Name in the Box Below
Select a Customer: Alfreds Futterkiste North/South Wolski ZajazdCustomer info will be listed here.
AJAX Example Explained
The example above contains a simple HTML form and a link to a JavaScript:
<html>
<head>
<script src="selectcustomer.js"></script>
</head>
<body>
<form>
Select a Customer:
<select name="customers" onchange="showCustomer(this.value)">
<option value="ALFKI">Alfreds Futterkiste
<option value="NORTS ">North/South
<option value="WOLZA">Wolski Zajazd
</select>
</form>
<p>
<div id="txtHint"><b>Customer info will be listed here.</b></div>
</p>
</body>
</html>
As you can see it is just a simple HTML form with a drop down box called "customers".
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 "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 JavaScript code is listed below.
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()
{
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;
}
The AJAX Server Page
The server page called by the JavaScript, is a simple ASP file called "getcustomer.asp".
The 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 an SQL against a database and returns the result as 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>")
%>
