Question

我想在加入2个表后显示唯一的行：

图书

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

在作者表中多次发现BookId时，预期的结果是显示最后一个ID（最后一个条目）：

我的实际LINQ代码

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

实际结果

BookId   AuthorId
12       1 
13       2
13       3
14       NULL

预期结果

BookId   AuthorId
12       1 
13       3
14       NULL

谢谢

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 };

Fiddle Me

Answer 2

尝试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

使用LINQ忽略重复的行

2 个答案: