public class EmployeeCustomizer implements DescriptorCustomizer {
 
    @Override
    public void customize(ClassDescriptor descriptor) throws Exception {
        // Direct (basic) query for the Oracle DB's ROWID value
        descriptor.addDirectQueryKey("rowId", "ROWID");
 
        // 1:M query accessing all projects which have a M:1 teamLeader reference to this employee
        // this can also be used to allow querying of large collections not wanted mapped
        OneToManyQueryKey projectsQueryKey = new OneToManyQueryKey();
        projectsQueryKey.setName("leadProjects");
        projectsQueryKey.setReferenceClass(Project.class);
        ExpressionBuilder builder = new ExpressionBuilder();
        projectsQueryKey.setJoinCriteria(builder.getField("PROJECT.LEADER_ID").equal(builder.getParameter("EMPLOYEE.EMP_ID")));
        descriptor.addQueryKey(projectsQueryKey);
    }
 
}

TypedQuery<Employee> query = em.createQuery("SELECT e FROM Employee e WHERE e.leadProjects IS NOT EMPTY", Employee.class);
return query.getResultList();