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:
Example
Customer info will be listed here... like:
| CustomerID | ALFKI |
| CompanyName | Alfreds Futterkiste |
| ContactName | Maria Anders |
| Address | Obere Str. 57 |
| City | Berlin |
| PostalCode | 12209 |
| Country | Germany |
Example Explained - The showCustomer() Function
When a user selects a customer in the dropdown list above, a function called "showCustomer()" is executed. The function is triggered by the "onchange" event:
showCustomer
function showCustomer(str) {
var xhttp;
if (str == "") {
document.getElementById("txtHint").innerHTML = "";
return;
}
xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (xhttp.readyState == 4 && xhttp.status == 200) {
document.getElementById("txtHint").innerHTML = xhttp.responseText;
}
};
xhttp.open("GET", "getcustomer.asp?q="+str, true);
xhttp.send();
}
The showCustomer() function does the following:
- Check if a customer is selected
- Create an XMLHttpRequest object
- Create the function to be executed when the server response is ready
- Send the request off to a file on the server
- Notice that a parameter (q) is added to the URL (with the content of the dropdown list)
The AJAX Server Page
The page on the server called by the JavaScript above is an ASP file called "getcustomer.asp".
The server file could easily be rewritten in PHP, or some other server languages.
The source code in "getcustomer.asp" 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("/datafolder/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>")
%>
