NHibernate QueryOver projection into DTO... anyone know of a cleaner way?

hql_example.cs

            var orderHeaders = Session.CreateQuery(
                @"select new OrderHeader(o.OrderedOn, c.Name, e.FirstName || ' ' || e.LastName)
                    from Order o inner join o.Customer c inner join o.Employee e")
                .List<OrderHeader>();

queryover_example.cs

            Customer customer = null;
            Employee employee = null;

            var orderHeaders = Session.QueryOver<Order>()
                .JoinAlias(o => o.Customer, () => customer)
                .JoinAlias(o => o.Employee, () => employee)
                .Select(Projections.ProjectionList()
                    .Add(Projections.Property<Order>(o => o.OrderedOn))
                    .Add(Projections.Property(() => customer.Name))
                    .Add(Projections.Property(() => employee.FirstName))
                    .Add(Projections.Property(() => employee.LastName)))
                .List<Object[]>()
                // the following select is the .NET Select extension method on IEnumerable, not part of the QueryOver api
                .Select(values => new OrderHeader((DateTime)values[0], (string)values[1], (string)values[2] + " " + (string)values[3]));

Not sure if it will work, but try this:

    Customer customer = null;
    Employee employee = null;
    OrderHeader orderHeader = null;

    var orderHeaders = Session.QueryOver<Order>()
        .JoinAlias(o => o.Customer, () => customer)
        .JoinAlias(o => o.Employee, () => employee)
        .SelectList(list => list
            .Select(o => o.OrderedOn).WithAlias(() => orderHeader.OrderedOn)
            .Select(o => customer.Name).WithAlias(() => orderHeader.Name)
            .Select(o => employee.FirstName).WithAlias(() => orderHeader.FirstName)
            .Select(o => employee.LastName).WithAlias(() => orderHeader.LastName))
        .TransformUsing(Transformers.AliasToBean<OrderHeader>())
        .Future<OrderHeader>();

If you want to keep using the constructor for OrderHeader, I guess you can use the AliasToBeanConstructor transformer.

i prefer to stick with the constructor so the AliasToBeanConstructor approach might work... but i was hoping to get rid of the variable declarations for the aliases and to get NHibernate to do the string concatenation like it does with the HQL example

I guess you can do the string concatenation in the Select().