Question

为了教育目的,我试图将以下林克语从“Linq”一书改为VB.net。

原件C号

var list = 
  from book in SampleData.Books
  group book by new { book.Publisher.Name, book.Subject }
    into grouping
  select new {
    Publisher = grouping.Key.Publisher,
    Subject = grouping.Key.Subject,
    Book = grouping
  };

我的尝试:

Dim list = _books.GroupBy(Function(book) New With {.Publisher = book.Publisher.Name,
                                                    book.Subject}).
                  Select(Function(grouping) New With {.Publisher = grouping.Key.Publisher,
                                                      .Subject = grouping.Key.Subject,
                                                      .Books = grouping})

For Each item In list
  Console.WriteLine("Publisher:" & item.Publisher & ", Subject:" & item.Subject)
  For Each Book In item.Books
    Console.WriteLine("  " & Book.Title)
  Next
Next

产出如下:

Publisher:FunBooks, Subject:Fun  
  Funny Stories  
Publisher:Joe Publishing, Subject:Work  
  LINQ rules  
Publisher:Joe Publishing, Subject:Work  
  C# on rails  
Publisher:Joe Publishing, Subject:Fun  
  All your base are belong to us  
Publisher:FunBooks, Subject:Fun  
  Bonjour mon Amour

I expected, that the books "LINQ rules" and "C# on rails" are grouped as well as the books "Funny Stories" and "Bonjour mon Amour" because they have the same Publisher and Subject. My anonymous key consists a new object of two simple strings.

我已经尝试在SO中搜寻,但other or 答案不能解决我的问题。甚至一些密码翻译,例如 ttelerik 或。本案没有帮助。

Answer 1

问题是:

GroupBy(Function(book) New With {.Publisher = book.Publisher.Name,
                                  book.Subject})

这并不等同于C#版本,因为不幸的是,VB使用mutable<>em>,即匿名性质的财产,而变性财产则被视为 has法或平等行动的一部分。你们需要使两种特性成为“灰色”特性:

GroupBy(Function(book) New With {Key .Publisher = book.Publisher.Name,
                                 Key book.Subject})

然后,它应当做罚款。可在VB onMSDN 上读更多匿名类型。

Answer 2

While I applaud your efforts to translate the samples, we actually have all of the samples for LINQ in Action in C# and VB available for download from the Manning Site: http://www.manning.com/marguerie/. Also, we have added samples to the LinqPad samples to make it easy to try the samples and save your changes. See http://www.thinqlinq.com/Default/LINQ-In-Action-Samples-available-in-LINQPad.aspx for instructions on how to access that.

看来,你正在就例子5.06b开展工作。略微更新,我们的翻译是:

Dim query = _
  From book In SampleData.Books _
  Group book.Title By book.Publisher, book.Subject Into grouping = Group _
  Select _
    Publisher = Publisher.Name, _
    Subject = Subject.Name, _
    Titles = grouping

如果你想要利用Lambda syntax,你确实需要具体指明钥匙为@johnskeet表示:

Dim list = SampleData.Books.GroupBy(Function(book) New With { 
                          Key .Publisher = book.Publisher.Name, 
                          Key .Subject = book.Subject}). 
               Select(Function(grouping) New With {
                  .Publisher = grouping.Key.Publisher, 
                  .Subject = grouping.Key.Subject, 
                  .Books = grouping})

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