public BookLending returnBook(Book book, Customer customer) {
Query query = em.createNamedQuery("findLendingByCustomerAndBookId");
query.setParameter("book", book);
query.setParameter("customer", customer);
List<BookLending> bookLendings = query.getResultList();
if (bookLendings.isEmpty()) return null;
BookLending bookLending = (BookLending) bookLendings.get(0);
bookLending.setBookIsLended(false);
bookLending.setReturnDate(new GregorianCalendar().getTime());
em.persist(bookLending);
return bookLending;
}
