Are there any arithmetic operation projections in NHibernate?

Question

I would like to get this SQL from NHibernate:

SELECT SUM(color_pages) * SUM(total_pages)
FROM connector_log_entry
GROUP BY department_name

Answer 1

Arithmetic operators can be used in criteria queries via the VarArgsSQLFunction SQL function. In your particular case, this would look something like:

Session.QueryOver()
    .SelectList(list =>
        list.SelectGroup(m => m.DepartmentName)
            .WithAlias(() => dto.Department)
            .Select(Projections.SqlFunction(
                new VarArgsSQLFunction("(", "*", ")"),
                NHibernateUtil.Int32,
                Projections.Sum(m => m.TotalPages),
                Projections.Sum(m => m.ColorPages)))
            .WithAlias(() => dto.TotalColorPercentage))
    .TransformUsing(Transformers.AliasToBean());

This technique injects strings directly into the generated SQL, so you'll need to make sure the underlying database supports the operators you use.