Question

I use the following query to get a result set

var overlaps = from s in db.signups
               join u in db.users on new { userid = s.userid } equals new     { userid = u.studentid }
               join a in db.activities on new { activityid = s.activityid } equals new { activityid = a.id }
               where
                    s.userid != Convert.ToInt32(Request.Cookies["studentid"].Value) &&
                      (from signups in db.signups
                         where
                               signups.userid == Convert.ToInt32(Request.Cookies["studentid"].Value)
                             select new
                             {
                                 signups.activityid
                             }).Contains(new { s.activityid })
                        orderby
                          u.studentid
                        select new
                        {
                            a.name,
                            u.firstname,
                            u.lastname,
                            u.studentid,
                            u.email
                        };

I’m pretty new to LINQ so I actually wrote the Sql and then used Linqer to generate the LINQ, so if this can be done more efficiently then please let me know. Having said that, this is not the problem.

The problem is that when I do

foreach(var overlap in overlaps)
{
    //do something
}

it throws the object reference not set error. This is being run in an MVC 3 application.

However, when this is run in a Console application, it runs without issue; it just returns no results. I’ve tried using DefaultIfEmpty but just can’t find anything that addresses how to use this with anonymous types.

So
… is my approach correct?
If not, what should I do differently?

Thanks, in advance.

Answer 1

I don’t know if this is your problem, but your join syntax is really weird.

You don’t have to build anonymous types here, just compare directly.

join u in db.users on s.userid equals u.studentid
join a in db.activities on s.activityid equals a.id

Same with this:

select new
{
    signups.activityid
}).Contains(new { s.activityid })

Can be just:

select signups.activityid).Contains(s.activityid)

And why in the world do you want to redo all the work to convert the cookie parameter to an int over and over?

var studentId = Convert.ToInt32(Request.Cookies["studentid"].Value);
//use this instead now in the query, dont repeat yourself