Get the latest inserted ID

[GePraxa]

This is not working, as I have to?

<?php
if(isset($_POST['submit'])) {

$db = DB::getInstance();

$fields=array(
'var1' => $var1,
'var2' => $var2
);
if($db->insert('table',$fields)){
$yes[] = 'text';
}else{
$no[] = 'text';
}

$last_id = $db->lastId();
}
?>