AJAX Database Example

AJAX can be used for dynamic communication with a database.

AJAX Database Example

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

Example

Example Explanation - showCustomer() Function

When a user selects a customer from the dropdown list above, the function named "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)
  {
    // IE7+, Firefox, Chrome, Opera, Safari code
    xmlhttp=new XMLHttpRequest();
  }
  else
  {
    // IE6, IE5 code
    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 performs the following tasks:

• Checks if a customer has been selected
• Creates an XMLHttpRequest object
• Executes the created function when the server response is ready
• Sends the request to a file on the server
• Note that we add a parameter q (with the content of the input field) to the URL

AJAX Server Page

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

Writing the server file in PHP is also straightforward, or you can use other server-side languages. See the corresponding example written in PHP here.

The source code in "getcustomer.php" is responsible for querying the database and returning 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>")
%>