Question

I’ve been using Linq for about a year and I have only a rudemntary understanding of SQL. So the following problem might be trite, and I appologize for that now. But at work I’ve been asked to figure out the most performant way to use linq on the following sql. and I need some help.

I have a Client table and a ClientParticiaption table. The ClientParticiaption table identifies Clients that particpate in a special training program. I need to determine which Client’s are not participating in the special training program. Here’s the SQL that works:

SELECT *
FROM Client
WHERE ClientControlID NOT IN
(
  SELECT ClientControlID
  FROM ClientParticipation
)

I’m having trouble converting this to its equivalent linq statement. I think I should be using the Except operator but I’m not sure how in this case. Any thoughts would be very helpful.

Here’s what I’m currently doing, which works, but I suspect this is not very effecient. Note, I’m using Entity Framework and I may have incorrectly assumed that resolving this issue has nothing to do with EF.

IList<int> clientControlIDs =
    ClientArngmt.Select(
    cac => cac.ClientControlID ).ToList();

IList<int> particiaptionClientArngmtIDs =
    Participations.Select(
    cap => cap.ClientArngmtID ).ToList();

IEnumerable<int> notParticipatingClientArngmtIDs =
    clientArngmtIDs.Except(
    particiaptionClientArngmtIDs );

Answer 1

1st solution:

ClientArngmt
 .Where(c => !Participations.Select(p => p.ClientArngmtID).Contains(c.ClientControlID))
 .Select(c => c);

2nd solution:

Participations
 .Where(p => !p.Clients.Any()) // Just assuming Clients is the ObjectSet name for ClientArngmt
 .SelectMany(p => p.Clients)
 .Distinct(); // If you want to get them distinct