Count projections in NHibernate 1.2

For someone who got stuck with NHibernate 1.1 it was actually surprisingly hard to find much about projections. Before you had to do different queries for a COUNT or a SELECT and you couldn’t use ICriteria.

int count = (int) session.CreateQuery(string.Format(
 "SELECT COUNT(instance) FROM Login instance WHERE Role='{0}'",
 TransitLoginRole.Administrator.ToString()))
 .UniqueResult();

This is resolved with a projection.

int count = session.CreateCriteria(typeof(Login))
 .Add(Expression.Eq("Role", TransitLoginRole.Administrator.ToString()))
 .SetProjection(Projections.Count("Id"))
 .UniqueResult<int>();

IList<Login> logins = session.CreateCriteria(typeof(Login))
 .Add(Expression.Eq("Role", TransitLoginRole.Administrator.ToString()))
 .List<Login>();

Nice and easy.

Daniel Doubrovkine

Count projections in NHibernate 1.2