How can I get the top categories by join in LINQ? - linq

Question

I am working on classified ads project I am facing problem to get top categories where most ads are posted every category have sub category also.
I made query but it is working for sub category ads I want if any category have no sub category then parent category ads should counted.
var result = (from c in db.Category
join a in db.Ad on c.CategoryId equals a.CategoryId
where c.ParentId != null
group c by c.ParentId into g
select new { cat = g.Key, a = g.Count() })
.OrderBy(c => c.cat)
.OrderByDescending(a => a.a);
My Category Table is like this
CategoryId ----- ParentId -----Name
How can I do this?

Answer 1

I guess this could be done with separate queries:
Get a list of categories that don't have any parentId set:
var resultsWithoutSubs = from c in db.Category
where c.ParentId == null
&& !result.Any(r => cat == c.CategoryId)
select c;
Based on the list above, repeat the original query:
var counts = from c in resultsWithoutSubs
join a in dbAd on c.CategoryId equals a.CategoryId
group c by c.CategoryId into g
select new {cat = g. Key, a = g.Count};
Then you should be able to Union these the first and the last list and sort the results.

Answer 2

Try this:
var results = db.Category
.Join(db.Ad, cat => cat.CategoryId,
ad => ad.CategoryId, (cat, ad) => new { cat, ad } )
.Where (c => !dbCategory
.Any (d => c.cat.CategoryId == d.ParentId) && c.cat.ParentId == null)
.GroupBy (c => c.cat.CategoryId)
.Select (g => new
{ cat = g.Key, a = g.Count () }
);