Question

I am trying to select a table from my database based on top 5 values from another table and met a roadblock.

here is the version without the top 5 values :

from d in Deals
from f in FacebookUserCategories
from s in SubCategories
where s.FacebookCategoryId == f.FacebookCategoryId
&& f.FacebookUserId == 1437585390
orderby f.Count descending
select d

However , what i need is to select Deals based on the top 5 Ids from SubCategories table, meaning i have to use a Take operator.

The below linq will help me achieve this :

(from f in FacebookUserCategories
 from s in SubCategories
 where s.FacebookCategoryId == f.FacebookCategoryId
 orderby f.Count descending
 select s.Id).Take(5)

Is there anyway for me to select the Deals table which has a SubCategoryId as a join from here?

Just to recap…i could write the sql.. it would be like this :

SELECT t1.* FROM Deal t1
INNER JOIN (
SELECT TOP 5 t2.Id FROM FacebookUserCategory , SubCategory t2
WHERE FacebookUserId = '1437585390'
AND FacebookUserCategory.FacebookCategoryId = t2.FacebookCategoryId 
ORDER BY Count DESC) tbl
ON t1.SubCategoryId = tbl.Id

Answer 1

Try this, Use Join for all 3 tables, You use Join for only 2 tables, why not use Join for 3rd table also.

var result = from d in deals
             let top5Counts =
            (from f in FacebookUserCategories
             join s in SubCategories on f.FacebookCategoryId equals s.FacebookCategoryId
             where f.FacebookUserId == 1437585390
             orderby f.Count descending
             select s.Id).Take(5)
            where top5Counts.Contains(d.SubCategoryId.Value)
            select d;