Mybatis学习笔记（七）--关联查询，一对一，一对多

关联查询

改造User实体类

public class User implements Serializable {

	private static final long serialVersionUID = 1L;
	private Integer id;
	private String username;
	private String sex;
	private Date birthday;
	private String address;

	//一对多
	private List<Orders> ordersList;
。。。省略了get/set
}

改造Orders实体类

public class Orders  implements Serializable{
    /**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private Integer id;
    private Integer userId;
    private String number;
    private Date createtime;
    private String note;
    //一对一
    private User user;
...省略了get/set
}

一对一

编写Mapper.xml

<!-- 
	一对一映射 
	这里的一对一要使用的不是基本类型，这里需要手动映射类型，这里使用的是resultMaps
	type 是要映射的类型  也就是这里的orders这个类
	id  就是select中的resultMap的对应的值  
-->
<resultMap type="Orders" id="order">
	<id column="id" property="id"/>
	<result column="user_id" property="userId"/>
	<!-- 
		一对一的使用标签 
		property是orders中的User声明的那个名字  private User user;
		javaType是user对应的java类型
	-->
	<association property="user" javaType="User">
		<!-- id:声明主键，表示user_id是关联查询对象的唯一标识 -->
		<id column="user_id" property="id"/>
		<result column="username" property="username"/>
	</association>
</resultMap>
<select id="getOrdersList" resultMap="order">
	select o.id,o.user_id,o.number,o.createtime,o.note,u.username from orders o left join user u on o.user_id = u.id;
</select>

编写mapper接口

测试代码

//一对一
@Test
public void testGetOrdersList() throws Exception {
	String res = "SqlMapConfig.xml";
	InputStream inputSteam = Resources.getResourceAsStream(res);
	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputSteam);
	SqlSession sqlSession = sqlSessionFactory.openSession();
	OrdersMapper mapper = sqlSession.getMapper(OrdersMapper.class);
	List<Orders> ordersList = mapper.getOrdersList();
	for (Orders orders : ordersList) {
		System.out.println(orders);
		System.out.println(orders.getUser());
	}
}

测试结果

一对多

编写mapper接口

编写mapper.xml

<!-- 
	一对多的映射
 -->
 <resultMap type="User" id="user">
 	<id column="id" property="id"/>
 	<result column="username" property="username"/>
 	<result column="birthday" property="birthday"/>
 	<result column="sex" property="sex"/>
 	<result column="address" property="address"/>
 	<!-- 
 		一对多映射
 		property  这里是User类中的List的声明  ofType这里是List中的泛型类
 	-->
 	<collection property="ordersList" ofType="orders">
 		<id column="id" property="id"/>
 		<result column="number" property="number"/>
 		<result column="user_id" property="userId"/>
 		<result column="createtime" property="createtime"/>
 		<result column="note" property="note"/>
 	</collection>
 </resultMap>
 <select id="getUserList" resultMap="user">
 	select 
 	o.id,o.user_id,o.number,o.createtime,o.note,
 	u.username,u.birthday,u.sex,u.address 
 	from user u left join orders o on o.user_id = u.id;
 </select>

测试方法

//一对多
@Test
public void testGetUserList() throws Exception {
	String res = "SqlMapConfig.xml";
	InputStream inputSteam = Resources.getResourceAsStream(res);
	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputSteam);
	SqlSession sqlSession = sqlSessionFactory.openSession();
	OrdersMapper mapper = sqlSession.getMapper(OrdersMapper.class);
	List<User> userList = mapper.getUserList();
	for (User user : userList) {
		System.out.println(user);
		if(user.getOrdersList().size()>0) {
			for (Orders o : user.getOrdersList()) {
				System.out.println(o);
			}
		}
		
	}
}

测试结果

Mybatis学习笔记（七）--关联查询，一对一，一对多

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