//加入购物车
public ActionResult AddToShelf(Reader reader, Shelf shelf, int Id,
string returnUrl)
{
//根据Id获取Book(BookSummary的表单只传递了id参数)
Book book = repository.Books.FirstOrDefault(p => p.Id == Id);
//将该书放入书架
shelf.AddItem(book);
return(RedirectToAction("Index", new { returnUrl }));
}