Question

我是LINQ的新手。我已经尝试过几次，但我无法得到我想要的结果。请帮忙解决这个问题。 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。我无法找到以下问题的解决方案。有人可以帮忙吗？感谢。

表：

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

将列的值转换为一行

2 个答案: