public ObservableCollection <BorrowedBook> GetBorrowedBooks() { borroweds = new ObservableCollection <BorrowedBook>(); for (int i = 1; i <= BorrowedBookCRUD.getMaxId(); i++) { BorrowedBook bb = new BorrowedBook(i); if (bb.BCustomerId != -1) { borroweds.Add(bb); } } return(borroweds); }