Hibernate05_延迟加载多对多

心已赠人 2023-03-05 03:23 3阅读 0赞

**Hibernate05\_延迟加载多对多**

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**注：Hibernate的多对多查询延迟加载默认是开启的**  
**lazy的取值为：true(默认)，false, extra**

例：查询Course，加载对应的Account。

测试：

Configuration configuration = new Configuration().configure();
    SessionFactory sessionFactory = configuration.buildSessionFactory();
    Session session = sessionFactory.openSession();
    Course course = session.get(Course.class, 1);
    System.out.println(course);

结果：  
发送了一条SQL

Hibernate: 
        select
            course0_.id as id1_4_0_,
            course0_.name as name2_4_0_ 
        from
            t_course course0_ 
        where
            course0_.id=?
    Course [id=1, name=Java]

测试：

结果：  
发送了两条SQL

关闭默认的延迟加载  
Course.hbm.xml

Account.hbm.xml

再次测试：

结果：  
发送了三条SQL

Hibernate: 
        select
            course0_.id as id1_4_0_,
            course0_.name as name2_4_0_ 
        from
            t_course course0_ 
        where
            course0_.id=?
    Hibernate: 
        select
            accounts0_.cid as cid2_0_0_,
            accounts0_.aid as aid1_0_0_,
            account1_.id as id1_3_1_,
            account1_.name as name2_3_1_ 
        from
            account_course accounts0_ 
        inner join
            t_account account1_ 
                on accounts0_.aid=account1_.id 
        where
            accounts0_.cid=?
    Hibernate: 
        select
            courses0_.aid as aid1_0_0_,
            courses0_.cid as cid2_0_0_,
            course1_.id as id1_4_1_,
            course1_.name as name2_4_1_ 
        from
            account_course courses0_ 
        inner join
            t_course course1_ 
                on courses0_.cid=course1_.id 
        where
            courses0_.aid=?
    Course [id=1, name=Java]

测试：

结果：  
发送了三条SQL

查询Account同理！