select * from publisher
where id not in (
    select publisher_id from record
    where year = 2008 and month = 4
)

DetachedCriteria c = DetachedCriteria.For<Record>()
    .SetProjection(Projections.Property("Publisher"))
    .Add(Restrictions.Eq("Year", 2008))
    .Add(Restrictions.Eq("Month", 4));
session.CreateCriteria(typeof(Publisher))
    .Add(Subqueries.PropertyNotIn("Id", c))
    .List();