mybatis嵌套查询

public List<MyOrdersVO> queryMyOrders(@Param("paramsMap") Map<String, Object> map);

<resultMap id="myOrdersVO" type="com.imooc.pojo.vo.MyOrdersVO">
    <id column="orderId" property="orderId"/>
    <result column="createdTime" property="createdTime"/>
    <result column="payMethod" property="payMethod"/>
    <result column="realPayAmount" property="realPayAmount"/>
      <result column="postAmount" property="postAmount"/>
      <result column="orderStatus" property="orderStatus"/>
      <result column="isComment" property="isComment"/>

    <collection property="subOrderItemList"
                select="getSubItems"
                column="orderId"
                ofType="com.imooc.pojo.vo.MySubOrderItemVO">
      <result column="itemId" property="itemId"/>
      <result column="itemName" property="itemName"/>
      <result column="itemImg" property="itemImg"/>
        <result column="itemSpecId" property="itemSpecId"/>
        <result column="itemSpecName" property="itemSpecName"/>
        <result column="buyCounts" property="buyCounts"/>
        <result column="price" property="price"/>
    </collection>
  </resultMap>

  <select id="queryMyOrders" resultMap="myOrdersVO" parameterType="Map">
    SELECT
        od.id as orderId,
        od.created_time as createdTime,
        od.pay_method as payMethod,
        od.real_pay_amount as realPayAmount,
        od.post_amount as postAmount,
        os.order_status as orderStatus,
        od.is_comment as isComment
    FROM
        orders od
    LEFT JOIN
        order_status os
    on od.id = os.order_id
    WHERE
        od.user_id = #{paramsMap.userId}
    AND
        od.is_delete = 0
        <if test="paramsMap.orderStatus != null">
          and os.order_status = #{paramsMap.orderStatus}
        </if>
    ORDER BY
        od.updated_time ASC
  </select>
    
    
    <select id="getSubItems" parameterType="String" resultType="com.imooc.pojo.vo.MySubOrderItemVO">

      select
        oi.item_id as itemId,
        oi.item_name as itemName,
        oi.item_img as itemImg,
        oi.item_spec_name as itemSpecName,
        oi.buy_counts as buyCounts,
        oi.price as price
      from
        order_items oi
      where
        oi.order_id = #{orderId}

    </select>

public class MyOrdersVO {

    private String orderId;
    private Date createdTime;
    private Integer payMethod;
    private Integer realPayAmount;
    private Integer postAmount;
    private Integer isComment;
    private Integer orderStatus;

    private List<MySubOrderItemVO> subOrderItemList;
}

public class MySubOrderItemVO {

    private String itemId;
    private String itemImg;
    private String itemName;
    private String itemSpecName;
    private Integer buyCounts;
    private Integer price;

}