Linq嵌套分組

Question

我有一個項目的大表，我需要按類別，然後按年，然後按月組織他們。

項目具有CategoryID和日期屬性。

我能走到今天：

Dim Items = From Item In DB.Items _ 
     Group By CategoryID = Item.CategoryID _ 
     Into Categories = Group _ 
     Order By CategoryID 

但是，在我把：

 Group By Year = Year(Item.Dated) 

和

 Group By Month = Month(Item.Dated) 

最終的結果應該是這樣的：

For Each Category in Categories 
For Each Year in Category.Years 
    For Each Month in Year.Months 
    For Each Item in Month.Items 

    Next 
    Next 
Next 
Next 

感謝

Answer 1

閱讀本（也與此主題的更多信息）之後：

http://msdn.microsoft.com/en-us/vbasic/bb738024.aspx

我想出了：

Dim Items = From Item In DB.Items _ 
    Group Item By CatID = Item.CatID Into Group Select CatID, _ 
    YearGroups = From y In Group _ 
    Group y By YearKey = y.PubDate.Value.Year Into YearGroup = Group _ 
    Select Year = YearKey, _ 
    MonthGroups = From m In YearGroup _ 
     Group m By MonthKey = m.PubDate.Value.Month Into MonthGroup = Group _ 
     Select Month = MonthKey, MonthItems = MonthGroup