需要解釋有關LINQ羣組加入語法

Question

我不堅強的LINQ，但我想熟悉GroupJoin

在下面的代碼，我想了解

var result = authors.GroupJoin(books, 
           author => author.AuthorId, 
           book => book.AuthorId, 
           (author, booksByAuthor) => 
           new { Author = author.Name, Books = booksByAuthor }); 

這是從改寫這種加入到代碼

var result = from a in authors 
      join b in books on a.AuthorId equals b.AuthorId into booksByAuthor 
      select new { Author = a.Name, Books = booksByAuthor }; 

我通過在GroupJoin語法混淆。我知道表格的作者和書籍一起，但接下來幾行的含義是什麼？

例如，author => author.AuthorId，book => book.AuthorId是什麼意思？這兩條線是否相當於

on a.AuthorId equals b.AuthorId 

？

什麼是此行的意義：

(author, booksByAuthor) => new { Author = author.Name, Books = booksByAuthor } 

我可以讀/理解加入到語句，但具有與該GroupJoin一些困難。謝謝。

Answer 1

可能你會感到困惑，因爲這兩個例子對於同一件事物使用不同的別名。因此，讓我們解決這個問題：

var result = from a in authors 
      join b in books on a.AuthorId equals b.AuthorId into booksByAuthor 
      select new { Author = a.Name, Books = booksByAuthor }; 

和

var result = 
    // authors join books 
    authors.GroupJoin(books, 
    // on a.AuthorId equals b.AuthorId 
    a => a.AuthorId, b => b.AuthorId, 
    // select new { Author = a.Name, Books = booksByAuthor } 
    (a, booksByAuthor) => new { Author = a.Name, Books = booksByAuthor } 
); 

希望有所幫助。