Reputation: 71
I've got two entities, Users and Friendships which look like:
public class User
{
public int UserId { get; set; }
(...)
}
public class Friendship
{
public int SenderId { get; set; }
public int ReceiverId { get; set; }
(...)
}
And I would like to create simple query which in SQL would look like:
SELECT * FROM Users as U
INNER JOIN Friendships as F ON U.UserId = F.ReceiverId OR U.UserId = F.SenderId
Where U.Nick != VARIABLE
In other words I would like to select all friends of the user.
And I can't accomplish that. I've found solution where one creates two separate join queries with union and it works - but it's not efficient to create such query to db.
Upvotes: 7
Views: 3595
Reputation: 47036
Simply write:
from U in db.Users
from F in Friendships.Where(x => U.UserId == F.ReceiverId || U.UserId == F.SenderId)
where U.Nick != VARIABLE
select new {u, f};
Upvotes: 2
Reputation: 1504062
Joins in LINQ are always equijoins. Basically you need multiple from
clauses and a where
clause:
var query = from u in db.Users
where u.Nick != variable
from f in db.Friendships
where u.UserId == f.ReceiveId || u.UserId == f.SenderId
select ...;
Now in LINQ to Objects there are probably more efficient ways of doing this - but I'd expect a SQL-based LINQ provider to generate a query which has a good enough execution plan. It may not actually create a JOIN in the SQL, but I'd expect it to be the same execution plan as the join you've shown.
Upvotes: 6