// Update the argument Map, adding the amounts for each book that this client ever ordered
public void updateQuantityOfBooksOrdered(Map<Book, Integer> quantities) {
for (Orders order : getOrders()) {
for (OrderLine orderLine : order.getOrderLines()) {
Book book = orderLine.getBook();
Integer quantity = quantities.get(book);
if (quantity == null) {
quantity = orderLine.getQty();
} else {
quantity += orderLine.getQty();
}
quantities.put(book, quantity);
}
}
}
