public void ReturnBook(Borrowing bor)
        {
            try
            {
                dataContext.usp_return_book(bor.BookCopy.Book.ISBN, bor.Customer.CustomerID, bor.BookCopy.CopyID);
            }
            catch (Exception ex)
            {

                ShowErrorMessage(ex.Message);
            }
        }
        public List<Borrowing> GetAllBorrowings()
        {
            var query = from c in dataContext.get_all_borrows()
                        select new
                        {
                            ISBN = c.ISBN,
                            CopyID = c.CopyID,
                            CustomerID = c.CustomerID,
                            Name = c.Name
                        };
            List<Borrowing> borrowings = new List<Borrowing>();
            foreach (var item in query)
            {
                Book book = new Book();
                book.ISBN = item.ISBN;

                BookCopy bc = new BookCopy();
                bc.Book = book;
                bc.CopyID = item.CopyID;

                Customer cust = new Customer();
                cust.CustomerID = item.CustomerID;
                cust.Name = item.Name;

                Borrowing b = new Borrowing();
                b.BookCopy = bc;
                b.Customer = cust;

                borrowings.Add(b);
            }
            return borrowings;
        }