Possible Duplicate:
Equivalent of SQL ISNULL in LINQ?
I have 3 tables like this :
comment table :
commentId pid sid text vid
1 1 null comment 1 1
2 null 1 comment 2 1
3 2 null comment 3 1
student table
sid firstname lastname
1 john adam
2 joan adam
professor table :
pid firstname lastname
1 mark abram
2 sean hoak
I want to make a query so the result to return like this :
firstname lastname
mark abram
john adam
sean hoak
m
if (select query ==null) then (selec query 1) else select (query 2)
i tried the following :
if((select pid from comment==null)
then select student.firstname , student.lastname from student where sid in (select sid from comment where vid=1)
else
(select professor.firstname ,professor.lastname from professor where pid in (select pid from comment where vid=1)
but with no use
then others provided this solution queries
IsNull Query
SELECT ISNULL(P.firstname, s.firstname) AS Expr1,ISNULL(P.lastname, s.lastname) AS Expr2
FROM comment AS C
LEFT OUTER JOIN professor AS P ON P.ID = C.PID
LEFT OUTER JOIN student AS s ON s.ID = C.SID
WHERE (C.VID = 2)
COALESCE:
SELECT COALESCE(p.firstname, s.firstname), COALESCE(p.lastname, s.lastname)
FROM comment c
LEFT JOIN Professor p
ON c.pid = p.id
LEFT JOIN Student s
ON c.sid = s.id
WHERE c.vid = 2
both works fine in SQL Management , but in Linq with the:
ObjectQuery<string> results1 = context.CreateQuery<string>(query1, parameters)
I've tried to convert it my self to :
var qry = from c in ctx.comment
join p in ctx.professor
on c.PID equals p.ID into tree
join s in ctx.student
on c.SID equals s.ID into tree1
where c.VID == vID
from tmp in tree.DefaultIfEmpty()
from tmp1 in tree.DefaultIfEmpty()
select new
{
Firstnmae = tmp.firstname ?? tmp1.firstname,
LastName = tmp.lastname ?? tmp1.lastname
};
but it returns null
Any ideas please?
