Linq to Entities Count子查询

Question

Okay so I've got a bunch of places which users can rate (give a score). When fetching places I also want to know how many of my friends rated that place. Users become friends by sending requests.

FRIENDREQID -- ID of user that sent the request.
FRIENDRESPID -- ID of user that got the request
STATUS -- Status of the request. (Accepted / Pending)

This query does the job.

select 
    p.*,
    (
        select 
            count(*) 
        from 
            UserRatings ur, 
            Friends f 
        where 
            ur.PlaceId = p.PlaceId
            and (ur.UserId = f.FriendReqId and f.FriendRespId = @myUserId ) 
            or  (ur.UserId = f.FriendRespId and f.FriendReqId = @myUserId ) 
            and f.Status = 'A' 
    ) as FriendCount
from 
    Places p

I really struggled with coming up with a mutual query in linq to entities (I'm a beginner) and came up with this.

 var result = (from p in db.Places
                 select new PlaceDTO
                 {
                     PlaceId = p.PlaceId,
                     FriendRatingCount = (from f in db.Friends
                                          from ur in db.UserRatings
                                          where ur.PlaceId == p.PlaceId && 
                                                (ur.UserId == f.FriendReqId && f.FriendRespId == argUserId) ||
                                                (ur.UserId == f.FriendRespId && f.FriendReqId == argUserId) &&
                                                f.Status == "A" 
                                          select f).Count()
                 })

Is it my friend system model that makes this query a bit bulky? Anyone has any tip of approvements that can be done too make it more efficient, easily read?

Answer 1

One question - why are you recalculating friends for every query? You can figure out the friends, and put reference to them in the User object. It's much simpler to do

var friendPlaces = users.Friends.Reviews.Where(r => r.PlaceId == placeID);

or even better

var friendPlace= users.Friends.Select(GetPlacesReviewed).Where(p => p.Id == placeID);

than have every part of the application know about your basic DB structure. What happens when you have to change your schema in 2 months?