public class UnitOfWork : IDisposable
{
    private OrderContext db = new OrderContext();
    private BookRepository bookRepository;
    private OrderRepository orderRepository;
 
    public BookRepository Books
    {
        get
        {
            if (bookRepository == null)
                bookRepository = new BookRepository(db);
            return bookRepository;
        }
    }
 
    public OrderRepository Orders
    {
        get
        {
            if (orderRepository == null)
                orderRepository = new OrderRepository(db);
            return orderRepository;
        }
    }
 
    public void Save()
    {
        db.SaveChanges();
    }
 
    private bool disposed = false;
 
    public virtual void Dispose(bool disposing)
    {
        if (!this.disposed)
        {
            if (disposing)
            {
                db.Dispose();
            }
            this.disposed = true;
        }
    }
 
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }
}