How to return a list of specific type instead of List<Object[]> in Hibernate?

Question

I have tree of classes:

classA {  
      classB b;  
      classC c;
      .....
} 

I have HQL query like this:

Answer 1

If you use Hibernate 5.x, you can use a ResultTransformer, as, e.g., described in this blog post. Note that ResultTransformer will be @Deprecated in Hibernate 6.

Applied to your scenario:

List classDDTOs = entityManager
.createQuery(
    "SELECT a.field1, b.field2, c.field3, c.field4 " +
    "FROM a LEFT OUTER JOIN b ON a.id = b.fk " +
    "LEFT OUTER JOIN c ON b.id = c.fk")
.unwrap( org.hibernate.query.Query.class )
.setResultTransformer( 
    new ResultTransformer() {
        @Override
        public Object transformTuple(
            Object[] tuple, 
            String[] aliases) {
            return new classD(
                (Type1) tuple[0],
                (Type2) tuple[1],
                (Type3) tuple[1],
            );
        }

        @Override
        public List transformList(List collection) {
            return collection;
        }
    } 
)
.getResultList();

The above code assumes classD has a constructor classD(Type1, Type2, Type3).

An advantage of this approach is that it lets you define the ResultTransformer once and allows you to reuse it in all queries with the same result type.