AJAX Database

AJAX can be used for dynamic communication with a database.

AJAX Database Example

The following example will demonstrate how a web page can read information from a database using AJAX: Please select a customer from the dropdown list below:

Try it yourself »

Example Explained - The showCustomer() Function

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

function showCustomer(str) {
  var xmlhttp;
  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","/try/ajax/getcustomer.php?q="+str,true);
  xmlhttp.send();
}

The showCustomer() function does the following:

• Check if a customer is selected
• Create an XMLHttpRequest object
• Create the function to execute when the server response is ready
• Send the request off to a file on the server
• Notice that we add a parameter q to the URL (with the content of the input field)

AJAX Server Page

The server page called by the JavaScript above is a PHP file called "getcustomer.php".

It is easy to write a server file in PHP, or with other server languages. Let's look at the corresponding example in PHP.

The source code in "getcustomer.php" does a query on 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>")
%>

AJAX ASP/PHP

AJAX XML