nhibernate linq and let keyword

Question

Is this possible to use let keyword with nhibernate linq? I wrote

 posts = from post in postsRepository.GetPosts(name)
                    let commentsCount = (from c in NHUnitOfWork.CurrentSession.Linq<Comment>()
                 where c.Post.ID == post.ID
                 select c).Count()
                    select new ...

and in response I have NHibernate.QueryException: could not resolve property: post of: Sys.Domain.Entities.Post