我是LINQ to SQL的初学者。我试图在LINQ中使用带有SQL IN运算符的子查询。 我正在尝试将查询 friends_A 和 friends_B 作为子查询与帖子查询中的SQL IN运算符进行整合:
where p.UserName IN (friends_A)
where p.UserName IN (friends_B)
我不在乎是否将子查询内联或使用变量进行整合。
问题是:
如何将查询 friends_A 和 friends_B (内联或使用变量)与SQL IN运算符集成?
额外问题:如何从联盟订购整体结果(在var posts
中):
orderby p.DateAndTime
?
using (FacebookDataEntities entities = new FacebookDataEntities())
{
var friends_A = from f in entities.Friends
where f.Friend_A != User.Identity.Name
&& f.Friend_B == User.Identity.Name
select f.Friend_A;
var friends_B = from f in entities.Friends
where f.Friend_A == User.Identity.Name
&& f.Friend_B != User.Identity.Name
select f.Friend_B;
var posts = ((from p in entities.Posts
where p.UserName.ToLower() == User.Identity.Name
select new { p.UserName, p.DateAndTime, p.PostText })
.Union(from p in entities.Posts
where p.UserName IN (friends_A)
select new { p.UserName, p.DateAndTime, p.PostText })
.Union(from p in entities.Posts
where p.UserName IN (friends_B)
select new { p.UserName, p.DateAndTime, p.PostText }));
ListViewPosts.DataSource = posts.ToList();
ListViewPosts.DataBind();
}
答案 0 :(得分:1)
查看您的代码我认为这就是您所需要的。通过这种方式,你也可以避免工会。
var friends_A = from f in entities.Friends
where f.Friend_A != User.Identity.Name
&& f.Friend_B == User.Identity.Name
select f.Friend_A;
var friends_B = from f in entities.Friends
where f.Friend_A == User.Identity.Name
&& f.Friend_B != User.Identity.Name
select f.Friend_B;
var posts =
from p in entities.Posts
let userName = p.UserName.ToLower()
where
userName == User.Identity.Name ||
friends_A.Concat(friends_B).Contains(userName)
orderby
p.DateAndTime
select new
{
p.UserName,
p.DateAndTime,
p.PostText
};
答案 1 :(得分:0)
你能试试吗?
.Union(from p in entities.Posts
where friends_A.Any(f => f.Name == p.UserName)
select new { p.UserName, p.DateAndTime, p.PostText })
.Union(from p in entities.Posts
where friends_B.Any(f => f.Name == p.UserName)
select new { p.UserName, p.DateAndTime, p.PostText }));