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);
	}

 

//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);
		
	}