Mybatis中一对多的关联查询

女爷i 2022-12-10 01:21 111阅读 0赞

#### Mybatis中一对多的关联查询 ####

问题：  
一个user中有多个订单order。

改造user的pojo

public class User { 
    
    	private Integer id;
    	private String username;// 用户姓名
    	private String sex;// 性别
    	private Date birthday;// 生日
    	private String address;// 地址
    	
    	private List<Order> orders;
    	// .....
    }

编写user的映射文件

<resultMap type="user" id="user_order_map">
    	<id property="id" column="id" />
    	<result property="username" column="username" />
    	<result property="address" column="address" />
    	<result property="birthday" column="birthday" />
    	<result property="sex" column="sex" />
    	
    	<collection property="orders" ofType="com.itheima.mybatis.pojo.Order">
    		
    		<id property="id" column="oid"/>
    		
    		<result property="userId" column="id"/>
    		<result property="number" column="number"/>
    		<result property="createtime" column="createtime"/>
    		<result property="note" column="note"/>
    	</collection>
    </resultMap>
    
    <select id="getUserOrderMap" resultMap="user_order_map">
    	SELECT
    	u.`id`,
    	u.`username`,
    	u.`birthday`,
    	u.`sex`,
    	u.`address`,
    	u.`uuid2`,
    	o.`id` oid,
    	o.`number`,
    	o.`createtime`,
    	o.`note`
    	FROM
    	`user` u
    	LEFT JOIN `order` o
    	ON o.`user_id` = u.`id`
    </select>

测试程序：

@Test
    public void testGetUserOrderMap() { 
    	SqlSession sqlSession = SqlSessionFactoryUtils.getSqlSessionFactory().openSession();
    	//获取接口的代理实现类
    	UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    
    	List<User> list = userMapper.getUserOrderMap();
    	for (User user2 : list) { 
    		System.out.println(user2);
    		for (Order order : user2.getOrders()) { 
    			if(order.getId() != null){ 
    				System.out.println(" 此用户下的订单有：" + order);
    			}
    		}
    	}
    
    	sqlSession.close();
    }

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