Grails: Criteria + Subquery (DetachedCriteria)

sub_query.groovy

/*
Suppose we need a query searching for all Equipments that are not being used in any ServiceOrder.

It means, given the following query:

select this_.* 
from  equipment this_ 
where this_.status == 'enabled'
      and not exists (select so_.id as y0_ from service_order so_ where (so_.equipment_id=this_.id))
order by this_.serial_number asc;
*/

import org.hibernate.criterion.DetachedCriteria
import org.hibernate.criterion.Projections
import org.hibernate.criterion.Restrictions
import org.hibernate.criterion.Subqueries

def result = Equipment.createCriteria().list() {
  eq 'status', 'enabled'
  def subQuery = DetachedCriteria.forClass(ServiceOrder, 'so').with {
                        setProjection Projections.id()
                        add Restrictions.conjunction()
                              .add(Restrictions.eqProperty('so.equipment.id', 'this.id'))
  }
  add Subqueries.notExists(subQuery)
  order 'serialNumber', 'asc'
  maxResults(25)
  cache: true
}