Error in SQL to LINQ conversion, how to solve that? - sql

Question

I have a SQl query working fine, I need to convert it to LINQ and got some problems.
My working SQL query:
select d.UserID, d.Content, d.UpdateTime
from DiaryPosts as d
where d.UserID = 2
/* friends */
Union
select d.UserID, d.Content, d.UpdateTime
from DiaryPosts as d
join Friends as fr
on d.UserID = fr.FriendID
where fr.UserID = 2
/* following */
Union
select d.UserID, d.Content, d.UpdateTime
from DiaryPosts as d
join Followers as fl
on d.UserID = fl.UserID
where fl.FollowerID = 2
/* ordenando por UpdateTime desc */
order by 3 desc
What I tried based on my own previous question:
var friends = (from u in db.User
join f in db.Friends
on u.ID equals f.FriendID
where f.UserID == userset.ID
orderby u.Nickname
select new FriendsSet { ID = u.ID, Nickname = u.Nickname, Thumbnail = u.Thumbnail }).ToList();
var followers = (from u in db.User
join f in db.Followers
on u.ID equals f.FollowerID
where f.UserID == userset.ID
orderby u.Nickname
select new FriendsSet { ID = u.ID, Nickname = u.Nickname }).ToList();
var diaryPosts = (from d in db.DiaryPosts
join e in db.EstadosDeAlma
on d.EstadosDeAlmaID equals e.ID
join u in db.User
on d.UserID equals u.ID
where d.UserID == userset.ID
select new DiaryPostsSet {
PostID = d.ID,
EstadoDeAlmaID = e.ID,
EstadoDeAlma = e.Title,
Author = u.Nickname,
Thumbnail = u.Thumbnail,
UserID = u.ID,
IsDuplicated = d.IsDuplicated,
FriendID = d.FriendID,
FriendName = u.Nickname,
Time = d.UpdateTime,
MessagesCount = d.FriendMessages.Count(m => m.DiaryPostsID == d.ID)
}).Take(6).ToList();
var diaryPostsUnion = diaryPosts.Union(friends).Union(followers).OrderBy(d => d.UpdateTime);
The errors I get:
'System.Collections.Generic.List<MvcWebRole1.Models.DiaryPostsSet>' does not contain a definition for 'Union' and the best extension method overload 'System.Linq.ParallelEnumerable.Union<TSource>(System.Linq.ParallelQuery<TSource>, System.Collections.Generic.IEnumerable<TSource>)' has some invalid arguments
Instance argument: cannot convert from 'System.Collections.Generic.List<MvcWebRole1.Models.DiaryPostsSet>' to 'System.Linq.ParallelQuery<MvcWebRole1.Models.FriendsSet>'

Answer 1

You're trying to union a sequence of one type with a sequence of another type. That doesn't make sense - unions have to be over the same types, basically.
It's not really clear what you're trying to do here, but I suspect you don't want a union.
Oh, and if you want all of this to happen in the database, get rid of the ToList calls.
EDIT: Okay, it's hard to see exactly how your LINQ queries correspond to your SQL queries, but basically your "select" clauses should be something like:
from d in db.DiaryPosts
// stuff here
select new { UserID = d.ID, d.UpdateTime, d.Content }
Use the exact same anonymous type in each query - the same property names and types, in the same order - and you should be able to use the Union method.