Question

I’m having difficulty translating sql to linq syntax.

I have 2 tables (Category and CategoryListing) which reference each other with CategoryID. I need to get a list of all the CategoryID in Category Table and the Count of CategoryID for all corresponding matches in the CategoryListing table. If a CategoryID is not present in CategoryListing, then the CategoryID should still be returned – but with a frequency of 0.

The following sql query demonstrates expected results:

SELECT c.CategoryID, COALESCE(cl.frequency, 0) as frequency FROM Category c LEFT JOIN (     SELECT cl.CategoryID, COUNT(cl.CategoryID) as frequency      FROM CategoryListing cl     GROUP BY cl.CategoryID ) as cl ON c.CategoryID = cl.CategoryID WHERE c.GuideID = 1 

Answer 1

Not tested, but this should do the trick:

var q = from c in ctx.Category         join clg in              (                 from cl in ctx.CategoryListing                 group cl by cl.CategoryID into g                 select new { CategoryID = g.Key, Frequency = g.Count()}             ) on c.CategoryID equals clg.CategoryID into cclg         from v in cclg.DefaultIfEmpty()         where c.GuideID==1         select new { c.CategoryID, Frequency = v.Frequency ?? 0 };