How to convert this SQL query to LINQ or Lambda expression? - sql

Question

I have the following SQL query:
SELECT C.ID, C.Name FROM Category C JOIN Layout L ON C.ID = L.CategoryID
JOIN Position P ON L.PositionID LIKE '%' + CAST(P.ID AS VARCHAR) + '%'
WHERE P.Code = 'TopMenu'
and following data
Position:
ID Code
1 TopMenu
2 BottomMenu
Category
ID Name
1 Home
2 Contact
3 About
Layout
ID CategoryID PositionID
1 1 1
2 2 1,2
3 3 1,2
With the above data, is it possible to convert the SQL query to LINQ or Lambda expression?
Any help is appreciated!

Answer 1

This might do what you want:
Layout
.Where(x => Position
.Where(y => y.Code == "TopMenu")
.Select(y => SqlClient.SqlMethods.Like(x.PositionID, "%" + y.ID.ToString() + "%")
).Count() > 0
).Join(
Category,
x => x.CategoryID,
x => x.ID,
(o,i) => new { ID = i.ID, Name = i.Name }
)
Although you might want to materialize the 'Position' sub query to save on time like so:
var innerSubQuery = Position.Where(y => y.Code == "TopMenu");
Layout
.Where(x => innerSubQuery
.Select(y => SqlClient.SqlMethods.Like(x.PositionID, "%" + y.ID.ToString() + "%")
).Count() > 0
).Join(
Category,
x => x.CategoryID,
x => x.ID,
(o,i) => new { ID = i.ID, Name = i.Name }
);
I do, however, agree with Jon that to really make your life simpler you should change the way you're handling the many-to-many relationship by creating a 'Layout_Position' table.

Answer 2

Well, you won't be able to express the second join as a join, because it's not an equijoin, but this should do it:
from c in category
join l in layout on c.Id equals l.CategoryId
from p in position
where p.Id.Contains(l.PositionId)
select new { c.Id, c.Name };
Note that your "contains/LIKE" clause will give you bad results when you've got more than 9 positions. There are better approaches to many-to-many relations than using a comma-separated list. (Such as an intermediate table.)