AJAX database


AJAX can be used to communicate interactively with the database.

AJAX Database Example

The following example will demonstrate how a web page reads information from the database through AJAX:

Example


Customer info will be listed here...

Example explanation - HTML page

When When the user selects a customer in the drop-down list above, a function named "showCustomer()" is executed. This function is triggered by the "onchange" event:

<!DOCTYPE html>
<html>
<head>
<script>
function showCustomer (str)
{
if (str=="")
{
document.getElementById("txtHint").innerHTML="";
return;
}
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp. status==200)
{
document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","getcustomer.asp ?q="+str,true);
xmlhttp.send();
}
</script>
</head
<body>

<form>
<select name="customers" onchange="showCustomer(this.value)">
<option value="">Select a customer:</option>
<option value="ALFKI">Alfreds Futterkiste</option>
<option value="NORTS ">North/South</option>
<option value="WOLZA"> ;Wolski Zajazd</option>
</select>
</form>
<br>
<div id="txtHint">Customer info will be listed here. ..</div>

</body>
</html>

Source code explanation:

If no customer is selected (str.length==0), then this function will clear the txtHint placeholder and then exit the function.

If a customer has been selected, the showCustomer() function performs the following steps:

  • Creates an XMLHttpRequest object

  • Create a function that executes when the server response is ready

  • Send a request to a file on the server

  • Note the parameters added to the end of the URL (q ) (Contains the contents of the drop-down list)

ASP file

The server page called through JavaScript in the above paragraph is an ASP named "getcustomer.asp" document. The source code in

"getcustomer.asp" runs a query against the database and returns the results 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>")
%>