用户表和订单表的关系为,一个用户有多个订单,一个订单只从属于一个用户,一对多查询的需求:查询一个用户,与此同时查询出该用户具有的订单
对应的sql语句:select *,o.id oid from user u left join orders o on u.id=o.uid;
1)修改User实体
public class Order {
private int id;
private Date ordertime;
private double total;
//代表当前订单从属于哪一个客户
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表当前用户具备哪些订单
private List<Order> orderList;
}
2)创建UserMapper接口
public interface UserMapper {
List<User> findAll();
}
3)配置UserMapper.xml
<mapper namespace="com.itheima.mapper.UserMapper">
<resultMap id="userMap" type="user">
<id column="uid" property="id"></id>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<!--配置集合信息
property:集合名称
ofType:当前集合中的数据类型
-->
<collection property="orderList" ofType="order">
<!--封装order的数据-->
<id column="oid" property="id"></id>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="userMap">
SELECT *,o.id oid FROM USER u,orders o WHERE u.id=o.uid
</select>
</mapper>
4)测试结果
@Test
public void test2() throws IOException {
InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> userList = mapper.findAll();
for (User user : userList) {
System.out.println(user);
}
sqlSession.close();
}
原文地址:https://www.cnblogs.com/nanao/p/15698363.html
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