06.Mybatis關聯查詢

1.一對一關聯查詢

　　需求：查詢出每條orders記錄和其關聯的user信息

在orders實體類中添加屬性與set、get方法

    /**
     * 測試1對1關聯查詢
     */
    private User user;
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }

接口：

public interface OrdersMapper {

    /**
     * 測試1對1關聯查詢
     */
    public List<Orders> findAllOrdersCNUser();
    
}

映射：

    <!-- 1對1的返回map
        不能省略映射，必須把全部想要查詢出來的屬性都手動映射
     -->
    <resultMap type="Orders" id="orders">
        <id property="id" column="id"/>
        <result property="userId" column="user_id"/>
        <result property="number" column="number"/>
        <result property="createtime" column="createtime"/>
        <result property="note" column="note"/>
        <!-- 1對1屬性 -->
        <!-- javaType必須寫！！ -->
        <association property="user" javaType="user">
            <id property="id" column="id"/>
            <result property="username" column="username"/>
            <result property="sex" column="sex"/>
            <result property="birthday" column="birthday"/>
            <result property="address" column="address"/>
        </association>
    </resultMap>
    
    <!-- 測試一對1關聯查詢 -->
    <select id="findAllOrdersCNUser" resultMap="orders">
        select
        *
        from 
        orders o left join user u
        on o.user_id=u.id
    </select>

測試：

    /**
     * 1對1關聯查詢
     */
    @Test
    public void m01() {
        // 獲取sqlSession,和Spring整理後由Spring管理
        SqlSession sqlSession = this.sqlSessionFactory.openSession();
        // 從sqlSession中獲取Mapper接口的代理對象
        OrdersMapper ordersMapper = sqlSession.getMapper(OrdersMapper.class);

        // 執行查詢
        List<Orders> list = ordersMapper.findAllOrdersCNUser();
        for (Orders orders : list) {
            System.out.println(orders);
            System.out.println(orders.getUser());
        }

        // 和Spring整理後由Spring管理
        sqlSession.close();
    }

2.一對多關聯查詢

　　需求：查詢出全部的user和與其對應的orders信息

在user實體類中添加屬性和set、get方法

    /**
     * 測試1對多
     */
    List<Orders> ordersList;
    public List<Orders> getOrdersList() {
        return ordersList;
    }
    public void setOrdersList(List<Orders> ordersList) {
        this.ordersList = ordersList;
    }

接口：

    /**
     * 測試1對多
     */
    public List<User> findAllUserCNOrders();

映射：

    <!-- 1對多返回映射 -->
    <resultMap type="User" id="user">
        <id property="id" column="id" />
        <result property="username" column="username" />
        <result property="sex" column="sex" />
        <result property="birthday" column="birthday" />
        <result property="address" column="address" />

        <!-- javaType && ofType必須寫！！ -->
        <collection property="ordersList" javaType="List" ofType="Orders">
            <id property="id" column="id" />
            <result property="userId" column="user_id" />
            <result property="number" column="number" />
            <result property="createtime" column="createtime" />
            <result property="note" column="note" />
        </collection>
    </resultMap>

    <!-- 測試1對多 -->
    <select id="findAllUserCNOrders" resultMap="user">
        select * from
        user u
        left join orders o
        on u.id = o.user_id
    </select>

測試：

    /**
     * 測試1對多
     */
    @Test
    public void m01() {
        // 獲取sqlSession,和Spring整理後由Spring管理
        SqlSession sqlSession = this.sqlSessionFactory.openSession();
        // 從sqlSession中獲取Mapper接口的代理對象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        // 執行查詢
        List<User> list = userMapper.findAllUserCNOrders();
        for (User user : list) {
            System.out.println(user);
            System.out.println(user.getOrdersList());
        }

        // 和Spring整理後由Spring管理
        sqlSession.close();
    }