Query: GroupBy Where Aggregate translation to server

Currently if there is predicate after grouping and before applying Aggregate operation we block the translation to server and do streaming GroupBy. Aggregate operator argument can take Case Block to do conditional aggregate and allow us to generate Group By clause in SQL. Structure would be

COUNT(
    CASE 
        WHEN predicate 
        THEN projection
        ELSE NULL
    END
)

[AlekseyMartynov]

Hello @smitpatel I recently stumbled upon this issue and found that there is a family of equivalent aggregates:

1. .GroupBy(o => o.OrderDate)
   .Select(g => g.Count(i => i.OrderDate != null))
   

2. .GroupBy(o => o.OrderDate)
   .Select(g => g.Where(i => i.OrderDate != null).Count())
   

3. .GroupBy(o => o.OrderDate)
   .Select(g => g.Select(i => i.OrderDate != null ? 1 : 0).Sum())
   

4. .GroupBy(o => o.OrderDate)
   .Select(g => g.Select(i => i.OrderDate != null ? (int?)1 : null).Sum())
   

(maybe more?)

Please support them all in the context of this feature. This code from NHibernate seems relevant and useful.

[smitpatel]

@AlekseyMartynov - Thanks for information. All of them are normalized into single form in our query parser so shouldn’t be issue in supporting them all.