Question

I am using Linq to Sql as my ORM and I have a list of Ids (up to a few thousand) passed into my retriever method, and with that list I want to grab all User records that correspond to those unique Ids. To clarify, imagine I have something like this:

List<IUser> GetUsersForListOfIds(List<int> ids)
{
        using (var db = new UserDataContext(_connectionString))
        {
            var results = (from user in db.UserDtos
                           where ids.Contains(user.Id)
                           select user);

            return results.Cast<IUser>().ToList();
        }
}

Essentially that gets translated into sql as

select * from dbo.Users where userId in ([comma delimmited list of Ids])

I’m looking for a more efficient way of doing this. The problem is the in clause in sql seems to take too long (over 30 seconds).

Answer 1

Will need more information on your database setup like index’s and type of server (Mitch Wheat’s post). Type of database would help as well, some databases handle in clauses poorly.

From a trouble shooting standpoint…have you isolated the time delay to the sql server? Can you run the query directly on your server and confirm it’s the query taking the extra time?

Select * can also have a bit of a performance impact…could you narrow down the result set that’s being returned to just the columns you require?

edit: just saw the ‘view comment’ that you added…I’ve had problems with view performance in the past. Is it a materialized view…or could you make it into one? Recreating the view logic as a stored procedure may aslo help.