Grails groupProperty和订单。这个怎么运作？

class Participation {
   ParticipationStatus status
}
class ParticipationStatus{
   String name
   Date creationDate
}

Participation.createCriteria().list{
   createAlias("status","statusAlias")
   order "statusAlias.creationDate"
   projections{
     groupProperty "id"    
   }
}

projections

groupProperty

projections

Participation.createCriteria().list{
   createAlias("status","statusAlias")
   order "statusAlias.creationDate"
   projections{
     groupProperty "id"    
     groupProperty "statusAlias.creationDate"
   }
}