VB.NET GroupBy LINQ语句 [英] VB.NET GroupBy LINQ statement

问题描述

我有一个时间让这个工作。我有一个 List（Of MyItem）名为 Items ，它们有一个 OrderId 属性。从这些项目中，我想创建一个 Order s的列表。一些项目将具有相同的 OrderId ，所以我想尝试按 OrderId 进行分组。然后我想按日期排序。这是我到目前为止：

 公共ReadOnly属性AllOrders（）作为列表（订单）
获取
 Return Items.Select（Function（i As MyItem）New Order（i.OrderID））_ 
 .GroupBy（Function（o As Order）New Order（o.OrderID））_ 
 .OrderBy （Function（o As Order）o.DateOrdered）.ToList 
 End Get 
 End Property 
  

当然，这不会编译，并且出现错误：
$ b

类型为'System.Collections'的值。 Generic.List（Of System.Linq.IGrouping（ Of Order，Order ））'不能转换为'System.Collections.Generic.List（ Of Order ））'

我粗体显示了我认为问题所在的部分，但我不知道如何解决此问题。此外，它还用于在添加 .GroupBy 语句之前正常工作（除了有重复的值）。任何人有任何想法？

谢谢

编辑

基本上，我想要：

现有商品清单列表并将其转换为
清单MyItem）：List（Of Order）：
 ItemId OrderId OrderID 
 1 100 100 
 2 102 102 
 3 100 
 

解决方案

你不需要为此使用group by。

 公共ReadOnly属性AllOrders（）以列表形式（订单）
获取
返回Items.Select Function（i）i.OrderID）.Distinct.Select（Function（p）New Order（p））。ToList（）
 End 
 End Property 
  

如果您想通过订单上的OrderedDate进行订购，只需在ToList之前添加一个orderby子句即可。

 公共ReadOnly属性AllOrders（）As List（Of Order）
获取
返回Items.Select（Function（i）i.OrderID）.Distinct _ 
 .Select（Function（p）New Order（p））_ 
 .OrderBy（Function（s）s.DateOrdered）.ToList（）
 End 
 End Property 
  

I am having a bear of a time getting this to work. I have a List(Of MyItem) called Items that have a OrderId property on them. From those items, I want to create a list of Orders. Some items will have the same OrderId so I want to try to group by OrderId. I then want to sort by date. Here's what I have so far:

Public ReadOnly Property AllOrders() As List(Of Order)
    Get
         Return Items.Select(Function(i As MyItem) New Order(i.OrderID)) _
         .GroupBy(Function(o As Order) New Order(o.OrderID)) _
         .OrderBy(Function(o As Order) o.DateOrdered).ToList
    End Get
End Property

This, of course, doesn't compile, and I get the error:

Value of type 'System.Collections.Generic.List(Of System.Linq.IGrouping(Of Order, Order))' cannot be converted to 'System.Collections.Generic.List(Of Order))'

I've bolded the part where I think the problem is, but I have no idea how to fix it. Also, it used to work fine (except there were duplicate values) before I added the .GroupBy statement. Anyone have any ideas?

Thanks

EDIT

Basically, I want this:

List of Existing Items      Take List and Turn it into 
List(Of MyItem):                 List(Of Order):
ItemId  OrderId                    OrderID 
1       100                        100
2       102                        102
3       100

解决方案

You don't need to use group by for this.

Public ReadOnly Property AllOrders() As List(Of Order)
Get
     Return Items.Select(Function(i) i.OrderID).Distinct.Select(Function(p) New Order(p)).ToList()
End Get
End Property

If you want to order it by the OrderedDate on the order, just add an orderby clause before the ToList

Public ReadOnly Property AllOrders() As List(Of Order)
Get
     Return Items.Select(Function(i) i.OrderID).Distinct _
                 .Select(Function(p) New Order(p)) _
                 .OrderBy(Function(s) s.DateOrdered).ToList()
End Get
End Property

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