Optimizing LINQ to Sharepoint

Question

I have three lists on Sharepoint 2010 and I have working code that gets the lists and relates them. My problem is that it takes around 15 seconds to load my page. I am a rank beginner with LINQ to Sharepoint and LINQ in general. MY question is: Is there a way to make this code run faster?

                SeatingChartContext dc = new SeatingChartContext(SPContext.Current.Web.Url);
                EntityList<Seating_chartItem> seatCharts = dc.GetList<Seating_chartItem>("seating_chart");
                EntityList<UsersItem> users = dc.GetList<UsersItem>("users");
                EntityList<Excluded_usersItem> exusers = dc.GetList<Excluded_usersItem>("excluded_users");
               // EntityList<LogsItem> logs = dc.GetList<LogsItem>("logs");

                List<Seating_chartItem> seatList = (from seat in seatCharts where seat.Room == 0 where seat.Floor == floor select seat).ToList();
                List <UsersItem> usersList = (from user in users select user).ToList();
                List <Excluded_usersItem> xusersList = (from xuser in exusers select xuser).ToList();

                var results = from seat in seatList
                              join user in usersList on
                              seat.User_id equals user.User_id
                              where seat.Room == 0
                              where seat.Floor == floor
                              where !(from xuser in xusersList select xuser.User_id).Contains(user.User_id)
                              select new 
                                         {
                                             sid = seat.Seat_id,
                                             icon = seat.Icon,
                                             topCoord = seat.Top_coord,
                                             leftCoord = seat.Left_coord,
                                             name = user.Name,
                                             phone = user.Phone,
                                             mobile = user.Mobile,
                                             content = seat.Content
                                         };

The time this code takes is frustrating, to say the least.

Thanks.

Answer 1

One immediate thing: You are re-querying xusersList everytime within your join:

where !(from xuser in xusersList select xuser.User_id).Contains(user.User_id)

Instead just first extract the user ids only (since that is the only thing you need)

var xusersList = (from xuser in exusers select xuser.User_id).ToList();

then use it directly:

  where !xusersList.Contains(user.User_id)

Even better - determine the valid users before your query:

usersList = usersList.Where( user => !xusersList.Contains(user.User_id))
                     .ToList();

Now you can just completely remove this where condition from your query.

Also these where conditions seem to be unneeded:

where seat.Room == 0
where seat.Floor == floor

since you have filtered your seatList this way already.

Having said that you should log some performance data to see what actually takes the most time - is it acquiring the inital lists or your actual join/linq query?