Linq to SQL Where In Clause Causes Object not set to instance of object

Question

I have two tables, subscriptions and topics. Each subscription is related to a specific TopicID (PK for topics table). The first query works fine and retrieves the topicID's of all videos that were uploaded today.

The problem occurs when I try and then use the results of query1 as a where-in clause for query 2. I keep receiving object reference not set to instance of an object.

Query 1

IQueryable<int> topics = (from t in dataLayer.Videos
                  where SqlMethods.DateDiffDay(t.DateCreated, DateTime.Today) == 0
                 select t.TopicID).Distinct();

Query 2 (fails)

 IQueryable<Subscription> subs = from s in dataLayer.Subscriptions
                                     where topics.Contains(s.TopicID)
                                     select s;

The Linq query generated when it fails is {Table(Subscription).Where(s => value(EmailSubscribers+<>c__DisplayClass0).topics.Contains(s.TopicID))}

Any insight into this would be appreciated. I have looked at some samples around the net and they all seem to be identical to mine.

Answer 1

You might need to ToList() your first query so that it is definitely executed.