Hibernate version:2.1.6

I'm trying to create a select that return a column with the difference in days between two dates field.

After a couple hours trying to use HQL i give up and start to to solve the problem using CompositeUserType. It's work. I get all the rows with a columns showing the differece in days. My problem now is how to use the CompositeUserType in the HQL Query. I need to group the column and when i do that i get this error:

net.sf.hibernate.QueryException: path expression ends in a composite value


I'ts not possible to use composite user type in HQL?

I appreciate any help.

Thanks