jpa实现多对多的属性时查询的两种方法

@query（
SELECT User FROM User u JOIN Student s on s.id = u.id where u.name LIKE :name
）
User findallByName(@param(“name”)String name);

   Specification<Class> specification = new Specification<>(){
   @override
   public predicate toPredicate(Root<Class> root , CriteriaQuery<?> query ,CriteriaBuilder cb){
       List<Precidate> precidate = Lists.newArrayList<>();
       if(num>0){
       Predicate p1 = cb.equal(root.get("num").as(Integer.Class),count);
         precidate.add(p1);
       }
       if(channel > 0){
         ListJoin<User,Student> join= root.join(root.getModel().getList("student",student.class),JoinType.LEFT);
         Predicate p2 = cb.equal(join.get("id").as(Integer.Class));
         //这里面的join代表的是student，属于加入进来的部分，而不是链接表的全部结果；
         precidate.add(p2);
       }
       List<User> list = DAO.findAll(specification,new Sort(DESC,"id"));
}
}

SELECT t FROM Teacher t join t.students s join s.books b where b.name = 'a' 

SELECT t FROM teacher t where t.students.books.name = 'a' 

SELECT t FROM Teacher t,Student s,Book b where s.id in elements(t.students) and b.id in elements(s.books)