I'm making a forum system. A ForumCategory (e.g. Sport) has a collection of Forums (e.g. Running, Cycling...). A Forum has a collection of Threads. A Thread has a collection of Messages.

My problem is, I want Threads to be ordered by the date of the latest message, so i'm ordering a collection, Threads, by the top(date) of the subcollection, Messages.

Is it possible to use Order-by for this? I can't figure out how to, as there is a join involved.

Alternatively, can I add a property to Thread containing the date of the latest Message, and can anyone provide any guidance of how to do this? parhaps by using a property formula?

Many thanks