Question

我对这些简单的类有疑问：

public class Thread
{
    public string Title { get; set; }
    public ICollection<Post> Posts { get; set; }
}

public class Post
{
    public DateTime Posted { get; set; }
    public string Text { get; set; }
}

我想要一个LINQ查询，它将返回所有线程，按最新的顺序排序。假设有Threads和Posts的实体框架DbContext，如何编写它？分组很简单：

from t in Threads
group t.Posts by t into tg
select tg.Key;

但是如何根据最新的Post.Posted？

对线程进行排序

编辑 - 基于Jons答案的解决方案：

from t in Threads
from p in t.Posts
group p by t into tg
orderby tg.Max(p => p.Posted) descending 
select tg.Key

Answer 1

您可以使用：

from t in Threads
group t.Posts by t into tg
orderby tg.Max(post => post.Posted) // Order by the latest post per thread
select tg.Key;

如果你想要首先按照最近发布的帖子订购线程，那么显然可以使用descending。

Answer 2

您也可以尝试：

var orderedThread1 = from t in threads
                     from p in t.Posts
                     orderby p.Posted ascending 
                     select t;

var orderedThread2 = from t in threads
                     group t.Posts by t
                     into tp
                     orderby tp.Max(posts => posts.Max(p => p.Posted))
                     select tp.Key;

根据组对LINQ分组查询进行排序

2 个答案: