Hibernate之HQL多表查询

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多表的查询进行使用HQL语句进行查询，HQL语句和SQL语句的查询语法比较类似

• 内连接查询
  • 显示内连接
    • select * from customer c inner join orders o on c.cid = o.cno
  • 隐式内连接
    • select * from customers c.orders o where c.cid = o.cno;
• 外连接查询
  • 左连接查询
    • select * from customers c left join orders o on c.cid = o.cno
  • 右连接查询
    • select * from customer c right join orders o on c.cid = o.cno

  HQL 的多表查询

  • 迫切和非迫切
    • 非迫切返回结果是Object[]
    • 迫切连接返回的结果是对象，把客户的信息封装到客户的对象中，把订单信息封装到客户的set集合中。

  内连接查询

• 内连接使用 inner join，默认返回的是Object数组

Session session = HibernateUtils.getCurrentSession();
Transaction tr = session.beginTransaction();
List<Customer> list = session.beginTransaction();
Set<Customer> set = new HashSet<Customer>(list);
for(Customer customer:set){
	System.out.println(customer);
}
tr.commit();

迫切内连接 ：inner join fetch,返回的是实体对象

Session session = HibernateUtils.getCurrentSession();
Transaction tr = session.beginTransaction();
List<Customer> list = session.createQuery("from Customer c inner join fetch c.linkmans").list();
Set<Customer> set = new HashSet<Customer>(list);//去掉重复
for(Customer customer : set){
	System.out.println(customer);
}
tr.commit;

左外连接查询

左外连接：封装成List<Object[]>

迫切左外连接

Session session = HIbernateUtils.getCurrentSession();
Transaction tr = session.beginTransaction();
List<Customer> list = session.createQuery("from Customer c left join fetch c.linkmans").list();
for(Customer customer : set){
	System.out.println(customer);
}
tr.commit();