如何将此查询转换为 linq？

Question

I have this SQL query

SELECT TOP 1 
    DOCID, ACTOR_ID, ACTOR_ROLE, ACTION_ID 
FROM
    ex_DOCAction 
WHERE
    DOCID = 126251
GROUP BY
    DOCID, ACTOR_ROLE, ACTION_ID, ACTOR_ID
HAVING
    COUNT(ACTION_ID) = 1

I came up with this:

from x in _db.ex_DOCAction.Where(a => a.DOCID == request.DocId)
group x by new { x.DOCID, x.ACTOR_ROLE, x.ACTION_ID, x.ACTOR_ID } into grouped
where 

and I don't know how to translate

 HAVING COUNT(ACTION_ID) = 1

There are lots of similar questions here, but I didn't find any question where count() had a parameter.

Answer 1

I guess you can't translate that group by + uniqueness check directly into SQL. You can return a structure, where you calculate the amount of the unique Action_Id s

from x in _db.ex_DOCAction.Where(a => a.DOCID == request.DocId)
  group x by new { x.DOCID, x.ACTOR_ROLE, x.ACTION_ID, x.ACTOR_ID }
    into grouped
  select new {Key = grouped.Key, Count = (from y in grouped select y.ACTION_ID).Distinct().Count() };

Answer 2

A Group by create a two dimensional list: List>. To Top is the first member of List. See code below

var results = _db.ex_DOCAction
   .Where(a => (a.DOCID == request.DocId) && (a.ACTION_ID != null))
   .GroupBy(x => new { x.DOCID, x.ACTOR_ROLE, x.ACTION_ID, x.ACTOR_ID })
   .Select(x => x.First())
   .ToList();