java - why my criteriaQuery.select method is wrong in spring data jpa -


i writing spring data jpa using specification. idea give me error(red line): 

'select(javax.persistence.criteria.selection<? extends capture<?>>)' in 'javax.persistence.criteria.criteriaquery' cannot applied '(javax.persistence.criteria.root<cn.lvxg.po.classroom>)'

here code. please me!

the root subclass of selection. why code wrong?

i suffering problem.

    specification<student> specification = new specification<student>() {         public predicate topredicate(root<student> root,//                                      criteriaquery<?> criteriaquery,                                      criteriabuilder criteriabuilder) {             root<classroom> classroomroot = criteriaquery.from(classroom.class);             root<student> studentroot = criteriaquery.from(student.class);             criteriaquery.select(classroomroot)                     .distinct(true)                     .where(criteriabuilder.equal(studentroot,classroomroot.get("id")));             return criteriaquery.getrestriction();;          }      };     pageable pageable = new pagerequest(0, 5);     page<student> studentspage = jpaspecificationrepository.findall(specification, pageable);

should 1 root in query.


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