Hibernate05_延迟加载多对多

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：

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

结果：
发送了两条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=?
[Account [id=1, name=张三]]

关闭默认的延迟加载
Course.hbm.xml

<set name="accounts" table="account_course" lazy="false">
	<key column="cid"></key>
	<many-to-many class="com.blu.entity.Account" column="aid"></many-to-many>
</set>

Account.hbm.xml

<set name="courses" table="account_course" lazy="false">
	<key column="aid"></key>
	<many-to-many class="com.blu.entity.Course" column="cid"></many-to-many>
</set>

再次测试：

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：

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

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=?
[Account [id=1, name=张三]]

查询Account同理！