Hibernate表中的1+N的问题：1、所谓1+N的问题，意思是说我们希望查询一张表里面的数据，但是在执行sql语句时，会发生多条和另外对应表的sql语句。这样会降低数据库执行效率和性能。

2.解决1+N的问题的三种方式如下:

	//使用session.creatQuery的方式,在对应的类中设置@ManyToOne(fetch=FetchType.LAZY)
 	@Test
	public void testSelect1Topic() {
		Session session = sf.openSession();
		session.beginTransaction();
	 	//List t =(List) session.createCriteria(Topic.class).list();
	 	//
		List t =(List) session.createQuery("from Topic").list();
	    
	 	for (Topic to : t) {
	     System.out.println(to.getId() + "-" + to.getTitle());
		
		}
	 	session.getTransaction().commit();
		session.close();
		
	}
 	//在对应的类中设置@BatchSize中size的属性的值
 	 	@Test
 		public void testSelect2Topic() {
 			Session session = sf.openSession();
 			session.beginTransaction();
 		 	//List t =(List) session.createCriteria(Topic.class).list();
 		 	//
 			List t =(List) session.createQuery("from Topic").list();
 		    
 		 	for (Topic to : t) {
 		     System.out.println(to.getId() + "-" + to.getTitle());
 			
 			}
 		 	session.getTransaction().commit();
 			session.close();
 			
 		}
 	//使用join fetch
  	@Test
	public void testSelect3Topic() {
		Session session = sf.openSession();
		session.beginTransaction();
	 	//List  t =(List) session.createCriteria(Topic.class).list();
	 	List t =(List) session.createQuery("from Topic t left join fetch t.category c").list();
	    for (Topic to : t) {
	     System.out.println(to.getId() + "-" + to.getTitle());
		
		}
	 	session.getTransaction().commit();
		session.close();
		
	}