N+1 有关问题

N+1 问题

//N+1问题????...查询Student信息,如果需要Clazz信息,如果有很多班级的话,就会有很多条查询语句.public void testN1(){Session session = HibernateUtil.getSession();Transaction tr = session.beginTransaction();Query query = session.createQuery("from Student");List<Student> list = query.list();if(null != list || list.size() > 0){for(Student student:list){System.out.println("--------------------------");System.out.println(student.getStudentName()+":"+student.getClazz().getClazzName());}}tr.commit();HibernateUtil.closeSession(session);}

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//解决N+1问题  --- 强迫左连接(只有一次查询),性能优化问题public void testN(){Session session = HibernateUtil.getSession();Transaction tr = session.beginTransaction();Query query = session.createQuery("from Student stu left join fetch stu.clazz");List<Object> list = query.list();if(null != list || list.size() > 0){for(Object object:list){Student student = (Student)object;System.out.println(student.getStudentName()+":"+student.getClazz().getClazzName());}}tr.commit();HibernateUtil.closeSession(session);}