Question

我在LINQ中并不强大，但我正在努力熟悉GroupJoin

在以下代码中，我试图理解

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

从此连接重写为代码

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 };

我对GroupJoin中的语法感到困惑。我理解表格的作者与书籍相结合，但接下来的几行是什么意思？

例如，author => author.AuthorId，book => book.AuthorId的含义是什么？这两行是否相当于

on a.AuthorId equals b.AuthorId

这一行的含义是什么：

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

我可以阅读/理解Join into语句，但对GroupJoin有一些困难。感谢。

Answer 1

可能你会感到困惑，因为这两个例子对同一件事使用不同的别名。所以，请修复：

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 }
);

希望有所帮助。

需要有关LINQ GroupJoin语法的解释

1 个答案: