here is my sample class to why i want to nest.

include("class.db.php");

class Cart {

function getProducts() {

//this is how i do it now. 
//enter code here`but i dont want to redeclare for every method in this class. 
//how can i declare it in one location to be able to use the same variable in every method?
$db = new mysqlDB;


$query = $db->query("select something from a table");
return $query

}

}