Class user {
          static hasMany = [group:Team]
                    }

     class StudentProfile extends User {
               static hasMany = [lessons: Lesson]
                                       }

           Class Lesson {
         static belongsTo=[ student: StudentProfile]
                                       }

def listGroup = Lesson.createCriteria().list{

            projections {
                 student{groupProperty('group')}}
            count()
            avg('scale')
        }
        [sectionExec:sectionExec]