How To Count Associated Entities Without Fetching Them In Entity Framework

Question

I\'ve been wondering about this one for a while now, so I thought it would be worth using my first Stack Overflow post to ask about it.

Imagine I have a discussion with

Answer 1

If this isn't a one off, and you find yourself needing to count a number of different associated entities, a database view might be a simpler (and potentially more appropriate) choice:

1. Create your database view.

   Assuming you want all of the original entity properties plus the associated message count:

   CREATE VIEW DiscussionCategoryWithStats AS
   SELECT dc.*,
         (SELECT count(1) FROM Messages m WHERE m.DiscussionCategoryId = dc.Id)
             AS MessageCount
   FROM DiscussionCategory dc
   

   (If you're using Entity Framework Code First Migrations, see this SO answer on how to create a view.)

2. In EF, simply use the view instead of the original entity:

   // You'll need to implement this!
   DiscussionCategoryWithStats dcs = _repository.GetDiscussionCategoryWithStats(id);
   
   int i = dcs.MessageCount;
   ...