The problem here consists of translating a statement written in LINQ to SQL syntax into the equivalent for NHibernate. The LINQ to SQL code looks like so:

var whatevervar = from threads in context.THREADs
                          join threadposts in context.THREADPOSTs
                            on threads.thread_id equals threadposts.thread_id
                          join posts1 in context.POSTs
                            on threadposts.post_id equals posts1.post_id
                          join users in context.USERs
                            on posts1.user_id equals users.user_id
                          orderby posts1.post_time
                          where threads.thread_id == int.Parse(id)
                          select new
                          {
                              threads.thread_topic,
                              posts1.post_time,
                              users.user_display_name,
                              users.user_signature,
                              users.user_avatar,
                              posts1.post_body,
                              posts1.post_topic
                          };

It's essentially trying to grab a list of posts within a given forum thread. The best I've been able to come up with (with the help of the helpful users of this site) for NHibernate is:

var whatevervar = session.CreateQuery("select t.Thread_topic, p.Post_time, " +
                                              "u.User_display_name, u.User_signature, " +
                                              "u.User_avatar, p.Post_body, p.Post_topic " +
                                              "from THREADPOST tp " +
                                              "inner join tp.Thread_ as t " +
                                              "inner join tp.Post_ as p " +
                                              "inner join p.User_ as u " +
                                              "where tp.Thread_ = :what")
                                              .SetParameter<THREAD>("what", threadid)
                                              .SetResultTransformer(Transformers.AliasToBean(typeof(MyDTO)))
                                              .List<MyDTO>();

But that doesn't parse well, complaining that the aliases for the joined tables are null references. MyDTO is a custom type for the output:

public class MyDTO
{
    public string thread_topic { get; set; }
    public DateTime post_time { get; set; }
    public string user_display_name { get; set; }
    public string user_signature { get; set; }
    public string user_avatar { get; set; }
    public string post_topic { get; set; }
    public string post_body { get; set; }
}

I'm out of ideas, and while doing this by direct SQL query is possible, I'd like to do it properly, without defeating the purpose of using an ORM.

Thanks in advance!