Question

我是C＃和LINQ的新手，我正在使用Northwind数据库。我的视图显示了数据库中的所有订单而没有订购。我想根据联系人姓名（客户）和按字母顺序显示订单：例如，AVARIA以及该客户的所有订单。等等...

我想要这样的事情：

AVARIA

ORDER 1 OF AVARIA FROM DATABASE WITH ITS DETAILS 
ORDER 2 OF AVARIA FROM DATABASE WITH ITS DETAILS  
ORDER 3 OF AVARIA FROM DATABASE WITH ITS DETAILS  

BECUA

ORDER 1 OF BECUA FROM DATABASE WITH ITS DETAILS
ORDER 2 OF BECUA FROM DATABASE WITH ITS DETAILS  

and so on...

因为这显示了来自数据库的所有订单，没有任何订购，例如第一行中的客户X和订单，然后客户Y，然后客户X再次订购，依此类推。我试过这个：

public ActionResult Index()
{
    var orders = db.Orders.Include(o => o.Customer).Include(o => o.Employee).Include(o => o.Shipper);
    var list = orders.OrderBy(x => x.Customer.ContactName);

    return View(list.ToList());
}

但它引发了以下异常：

类型的例外＆＃39; System.Data.Entity.Core.EntityCommandExecutionException＆＃39;发生在 EntityFramework.SqlServer.dll但未在用户代码中处理

视图效果很好。

请帮忙。

Answer 1

你可以使用group by和orderby。样品：

class Program
{

    class grpitem
    {
        public string groupCode;
        public string item;
    }

    static List<grpitem> list = new List<grpitem>()
    {
         new grpitem() {groupCode="3", item="b"},
         new grpitem() {groupCode="1", item="b"},
         new grpitem() {groupCode="3", item="c"},
         new grpitem() {groupCode="2", item="b"},
         new grpitem() {groupCode="2", item="a"},
         new grpitem() {groupCode="2", item="c"},
         new grpitem() {groupCode="1", item="a"},
         new grpitem() {groupCode="3", item="a"},
         new grpitem() {groupCode="3", item="d"}
    };

    static void Main(string[] args)
    {
        IEnumerable<grpitem> ordered = list.GroupBy(grp => grp.groupCode)
            .SelectMany(g => g.OrderBy(grp => grp.item)).OrderBy(g => g.groupCode);

        foreach(grpitem g in ordered)
            Console.WriteLine("groupCode:{0} item:{1}",g.groupCode,g.item);

        Console.ReadLine();
    }
}

输出：

groupCode:1 item:a
groupCode:1 item:b
groupCode:1 item:c
groupCode:1 item:d
groupCode:2 item:a
groupCode:2 item:b
groupCode:3 item:a
groupCode:3 item:b
groupCode:3 item:c

Answer 2

您可以使用GroupBy（...）

public ActionResult Index()
{
    var orders = db.Orders.Include(o => o.Customer).Include(o => o.Employee).Include(o => o.Shipper);
    var groupedOrders = orders.GroupBy(o => Customer.Name, o => o);
    // grouped orders is IEnumerable<string, IEnumerable<Order>>
    return View(groupedOrders);
}

如何根据Customer ContactName对Northwind订单进行分组

2 个答案: