hibernate的多表查询

Posted 2021-01-11 奇迹再现

1.交叉连接

select  * from A ,B

2.内连接   可以省略inner join

   隐式内连接：

select * from A,B where A.id = B.aid;

   显式内连接：

select * from A inner join B on A.id = B.aid;

   迫切内连接：

需要加上fetch关键字

内连接查询两者共有的属性数据。

3.外连接 outer join

  左外连接：

select * from A left outer join B on A.id= B.aid;

  右外连接：

select * from A right outer join B on A.id = B.aid;

迫切左外连接：需要加上fetch关键字，返回的是对象，不再是数组。

外连接查询共有属性和一方连接的属性

 

Session session = HibernateUtils.getCurrentSession();
        Transaction tx = session.beginTransaction();
        // SQL:SELECT * FROM cst_customer c INNER JOIN cst_linkman l ON
        // c.cust_id = l.lkm_cust_id;
        // HQL:内连接 from Customer c inner join c.linkMans
        /*
         * List<Object[]> list = session.createQuery(
         * "from Customer c inner join c.linkMans").list(); for (Object[]
         * objects : list) { System.out.println(Arrays.toString(objects)); }
         */

        // HQL:迫切内连接 其实就在普通的内连接inner join后添加一个关键字fetch. from Customer c inner
        // join fetch c.linkMans
        List<Customer> list = session.createQuery("select distinct c from Customer c inner join fetch c.linkMans")
                .list();// 通知hibernate，将另一个对象的数据封装到该对象中

        for (Customer customer : list) {
            System.out.println(customer);
        }
        tx.commit();