$ _SESSION与Ajax

I have two php files.

addbasket.php

<?php    
session_start();   
$link = $_SESSION['link'];  
if (isset($_SESSION['userid'])) {......}
?>

and

index.php

<?php 
session_start();   
$_SESSION['link'] = mysqli_connect("localhost","test","test","dbname");  
$link = $_SESSION['link'];
.... 
?>

The file addbasket.php is called by Ajax and given Parameters for article (number) and amount (number)

but the mysqli_query doesnt work. It seems like the $_SESSION['link'] is not there in addbasket.php. It can't be the Session, because the $_SESSION['userid'] is there, right and can be echoed.

What could be the Problem here?

You can't serialize a resource object and that's why you can't hold it in the session

$_SESSION can only store serializable data.

mysqli_connect returns a resource. Resources are not serializable.

You'll have to instantiate that DB connection in every request.

Edit: OK, now I understand your actual problem. What you need is some form of this:

db.php

$link = mysqli_connect("localhost","test","test","dbname");

index.php

require 'db.php';
$r = mysqli_query($link, 'SOME QUERY...');
....

addbasket.php

require 'db.php';
$r = mysqli_query($link, 'SOME OTHER QUERY...');
....