Mybatis_多对一关联查询

订单表对人员表就是多对一。

在Orders.java类中加一行private Person person; 并生成setter getter。

在OrdersMapper.xml中写sql：

首先不要忘了在sqlMapConfig.xml中加入这一行：<mapper resource="xxx/x/mapper/OrdersMapper.xml" />

    <!-- 多对一查询
        association:多对一的时候用
        property:多对一中“一”的那个属性名
        javaType:property中那个变量的数据类型
    -->
    <resultMap type="xxx.x.Orders" id="selectPersonByOrderIdRM" extends="BaseResultMap">
        <association property="person" javaType="xxx.x.model.person">
            <id column = "person_id" property = "personId" />
            <result column = "name" property = "name" />
            <result column = "gender" property = "gender" />
            <result column = "person_addr" property = "personAddr" />
            <result column = "birthday" property = "birthday" />
        </association>
    </resultMap>
    
    <select id="selectPersonByOrderId" parameterType="int" resultMap="selectPersonByOrderIdRM">
        select * from orders o, person p where o.PERSON_ID = p.PERSON_ID and o.ORDER_ID = #{orderId}
    </select>

    SqlSessionFactory sessionFactory;
    public void setUp() throws Exception {
        InputStream in = Resources.getResourceAsStream("sqlMapConfig.xml");
        sessionFactory = new SqlSessionFactoryBuilder().build(in);
    }
    public void selectPersonByOrderId() {
        // 创建SqlSession
        SqlSession session = sessionFactory.openSession();
        try {
            Orders order = session.selectOne("xxx.x.mapper.OrdersMapper.selectPersonByOrderId", 1);
            System.out.println(order);
        } catch (Exception e) {
            e.printStackTrace();
            session.rollback();
        } finally {
            session.close();
        }
    }