使用LINQ忽略重復的行

Question

我想在加入2個表后顯示唯一的行：

書

Id        Title
12        Title 1
13        Title 2
14        Title 3

作者

Id  BookId    Name
1   12        Steeve
2   13        Michel
3   13        Robert

在作者表中多次發現BookId時，預期的結果是顯示最后一個Id（最后一個條目）：

我的實際LINQ代碼

from book in Books
join author in Authors on book.Id equals author.BookId into gr1
from join1 in gr1.DefaultIfEmpty()

實際結果

BookId   AuthorId
12       1 
13       2
13       3
14       NULL

預期結果

BookId   AuthorId
12       1 
13       3
14       NULL

謝謝

Answer 1

方法如下：

var query = from book in Books
            join author in Authors on book.Id equals author.BookId into gr1
            select new { BookId = book.Id, AuthorId = gr1.LastOrDefault()?.Id };

小提琴

Answer 2

嘗試where子句

from book in Books
join author in Authors on book.Id equals author.BookId into gr1
from join1 in gr1.DefaultIfEmpty()
where author.authorID != null