Assuming we have an Order class with a member variable named customer of type User:
//get current user
UserService userService = UserServiceFactory.getUserService();
User user = userService.getCurrentUser();
PersistenceManager pm = PMF.get().getPersistenceManager();
String select_query = "select from " + Order.class.getName();
Query query = pm.newQuery(select_query);
query.setFilter("customer == paramCustomer");
List<OrderDTO> result= OrderUtils.getOrderDTOList((List<Order>) query.execute(user));
//feck-off --> I'll never get an MVP but I can swear on my blog!
Just wanted to share to spare some random googler (you) the same process.