LINQ到与子查询实体在选择部分 [英] Linq to Entities with Subselect in select part

问题描述

我们已经开始使用EF一个MVC项目。 我们需要使用子查询在LINQ中写了很多的查询，并且没有想出但如何能够做到这一点。

We are starting with a MVC project using EF. We will need write a lot of queries in LINQ using subselect and don't have figured out yet how this could be done.

这些最简单的例子就是以这种形式：

The most simple case of these is in this form:

select p.Id, 
       p.Title,
       (select count(*) 
          from Comments c
         where c.PostId = p.Id
       ) as CommentCount
  from Post p
 where p.UserId = 'John';

读101页的微软和堆栈溢出的例子我找不到这样的例子。 我发现采用加入和组的例子，但在某些情况下，已经是组中的查询。

Reading the "101 page" of examples from Microsoft and Stack Overflow I couldn't find a example like this. I found examples using join and group, but in some cases the are already a group in the query.

你能不能帮我解决这个疑问，请？ 谢谢你。

Can you help me with this query, please? Thanks.

推荐答案

您需要叫上发表评论导航属性（如果有指定的外键EF自动创建它），那么你可以使用查询作为下。

You will need a Navigation property called Comments on Post (EF automatically creates it if you have foreign keys specified) then you can use query as under.

from p in Context.Posts
where p.UserId == "John"
select new 
{
  Id = p.Id,
  Title = p.Title,
  Count = p.Comments.Count()
}

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