vb.net - 将一列的值转换为一行

Question

我是 LINQ 的新手。我尝试了几种方法，但我无法得到我想要的结果。请帮助解决这个问题。VB.NET 中的 LINQ to SQL。

我正在使用 Ling to SQL 类来运行查询以获得预期的结果。在查询结果之后，我将使用它来填充 Datagridview 。我找不到以下问题的解决方案。有没有人可以帮忙？谢谢。

桌子：

bookID  authorID  authorname
111     101       Mark
222     102       Tim
333     103       John
444     104       Rebecca
111     102       Tim
111     103       John
222     104       Rebecca

结果应该是：

bookID   author1     author2         author3....

111      Mark            Tim                  John

222      TIm              Rebecca          N/A or Empty

333      John            N/A or Empty    N/A or Empty

444      Rebecca      N/A or Empty    N/A or Empty

我必须只使用LINQ。

Answer 1

您可以使用该GroupBy方法执行此操作

Dim results = db.Books.GroupBy(Function(b) b.bookID, Function(b) b.authorname)

或者，如果您更喜欢 linq 查询语法

Dim results = _
    From b In db.Books _
    Group b.authorname By bookID = b.bookID Into authorname = Group

您可以将其用作

For Each group In results
    Console.Write(group.Key)
    Console.Write(":")
    For Each name As String In group 
        Console.Write("  " & name)
    Next 
    Console.WriteLine()
Next 

输出

111: Mark Tim John
222: Tim Rebecca
333: John
444: Rebecca

Answer 2

Dim results = From b In db.Books Group b.authorname _ 
                By bookID = b.bookID Into nameg = Group select bookid,nameg

For each gr in results 
    Console.Write(gr.bookid)
    Console.Write(":")
    For Each name As String In gr.nameg 
    Console.Write("  " & name)
Next 
Console.WriteLine()
Next