NHibernate Criteria left antijoin/ subquery confusion

Question

I'll preface this with the fact that NHibernate is well out of my comfort zone, so this may be much simpler than I'm making it out to be.

I have a users table and an events table mapped to user and event objects.

My event objects reference a singular user object.

I have a property that I persist on my user object for LastActivityTimeStamp.

I have properties on my event object related to EventType and Success.

To determine a list of users that are "online", I need to collect all user objects with a LastActivityTimeStamp greater than a previously calculated cutoff value, whose last activity in the events table was not a successful "Logoff" event type.

How would I write this criteria?

Answer 1

try to tweak this

var subquery = DetachedCriteria.For<Event>()
    .Add(Restrictions.Eq("Success", true))
    .Add(Restrictions.EqProperty("User.Id", "u.id"))
    .AddOrder(Order.Desc("TimeStamp"))
    .SetProjection(Projections.Property("EventType"))
    .SetMaxResults(1);

session.CreateCriteria<User>("u")
    .Add(Restrictions.Ge("LastActivityTimeStamp", cutoff))
    .Add(Subqueries.Ne(EventType.LogOff, subquery));