Ajax Database

AJAX can be used for interactive communication with a database.

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AJAX Database Example

The following example will demonstrate how a web page can fetch information from a database with AJAX:

Example Select a customer: Alfreds Futterkiste North/South Wolski Zajazd Customer info will be listed here...

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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:

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","getcustomer.asp?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 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)

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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. Look at a corresponding example in PHP.
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("/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>") %>