DTO里面的复合属性下，有1对多，怎么collection呢

比如：

public class GoodsDTO {

private Goods goods;

private Category category;

｝

但是 Goods 实体类里有： private List<GoodsDetail> goodsDetailList; // 商品详情

请问图示中的<resultMap>要怎么查询？

坨坨儿 2024-04-16

源自：MyBatis进阶 3-1 OneToMany对象关联查询

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1回答

好帮手慕小蓝回答被采纳获得+3积分 2024-04-16 11:23:01

同学你好，此时就需要先单独为Goods建立resultMap，例如：

<resultMap id="GoodsResultMap" type="com.imooc.Goods">  
    <id property="goodsId" column="goods_id" />  
    <result property="title" column="title" />  
    <!-- 映射Goods中的goodsDetailList集合 -->  
    <collection property="goodsDetails" select="goodsDetail.selectByGoodsId"
                    column="goods_id"/>
</resultMap>

然后在DTO中，引用这个resultMap即可，例如：

<resultMap id="GoodsDTOResultMap" type="com.imooc.GoodsDTO">  
    <association property="goods" resultMap="GoodsResultMap" />  
</resultMap>

祝学习愉快~

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坨坨儿提问者 #1

public class Goods {
    private Integer goodsId;             // 商品编号
    private String title;           // 标题
    private String subTitle;          // 子标题
    private Float originalCost;      // 原始价格
    private Float currentPrice;      // 当前价格
    private Float discount;          // 折扣率
    private Integer isFreeDelivery;  // 是否包邮，1-包邮 0-不包邮
    private Integer categoryId;      // 分类编号
    private List<GoodsDetail> goodsDetailList;      // 商品详情
    private List<GoodsCover> goodsCoverList;        // 商品封面
    private List<GoodsParam> goodsParamList;        // 商品参数
}

goods.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="goods">
    <resultMap id="rmGoodsHaveMany" type="com.imooc.mybatis.entity.Goods">
        <result property="goodsId" column="goods_id"/>
        <collection property="goodsDetailList" select="goodsDetail.selectByGoodsId" column="goods_id"/>
        <collection property="goodsCoverList" select="goodsCover.selectByGoodsId" column="goods_id"/>
        <collection property="goodsParamList" select="goodsParam.selectByGoodsId" column="goods_id"/>
    </resultMap>
    <select id="selectGoodsHaveMany" resultMap="rmGoodsHaveMany">
        select * from t_goods limit 0,5
    </select>
 
    <resultMap id="rmGoodsDTOHaveMany" type="com.imooc.mybatis.entity.Goods">
        <result property="goods.goodsId" column="goods_id"/>
        <result property="goods.title" column="title"/>
        <result property="goods.subTitle" column="sub_title"/>
        <result property="goods.originalCost" column="original_cost"/>
        <result property="goods.currentPrice" column="current_price"/>
        <result property="goods.discount" column="discount"/>
        <result property="goods.isFreeDelivery" column="is_free_delivery"/>
        <result property="goods.categoryId" column="category_id"/>
        ???怎么写？goodsDetailList
        ???怎么写？goodsCoverList
        ???怎么写？goodsParamList
        <result property="category.categoryId" column="category_id"/>
        <result property="category.categoryName" column="category_name"/>
        <result property="category.parentId" column="parent_id"/>
        <result property="category.categoryLevel" column="category_level"/>
        <result property="category.categoryOrder" column="category_order"/>
    </resultMap>
    <select id="selectGoodsDTOHaveMany" resultMap="rmGoodsDTOHaveMany">
        select g.*,c.* from t_goods as g join t_category c on g.category_id = c.category_id
        order by g.goods_id limit 0,20
    </select>
</mapper>

goods-detail.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="goodsDetail">
    <select id="selectByGoodsId" parameterType="Integer" resultType="com.imooc.mybatis.entity.GoodsDetail">
        select * from t_goods_detail where goods_id = #{value}
    </select>
</mapper>

goods-cover.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="goodsCover">
    <select id="selectByGoodsId" parameterType="Integer" resultType="com.imooc.mybatis.entity.GoodsCover">
        select * from t_goods_cover where goods_id=#{value}
    </select>
</mapper>

goods-param.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="goodsParam">
    <select id="selectByGoodsId" parameterType="Integer" resultType="com.imooc.mybatis.entity.GoodsParam">
        select * from t_goods_param where goods_id=#{value}
    </select>
</mapper>

1、在goods.xml文件中执行商品查询，因为是单表查询，无需DTO，建立1对多的映射，执行没有问题【id="selectGoodsHaveMany"】

2、在goods.xml文件中执行商品表和分类表关联查询，结果集用DTO保存，而DTO中的商品又需要级联查询，此时，映射有问题【id="selectGoodsDTOHaveMany"】

3、上述代码应该可以复制粘贴运行，我在goods.xml文件中标注了有三行？？？,请老师帮忙看看那三行？处，要如何获取这3个复合属性？

2024-04-16 12:00:27

坨坨儿提问者 #2

更正一下：good.xml文件中，
原内容：<resultMap id="rmGoodsDTOHaveMany" type="com.imooc.mybatis.entity.Goods">
改内容：<resultMap id="rmGoodsDTOHaveMany" type="com.imooc.mybatis.entity.GoodsDTO">
GoodsDTO实体类代码如下:
1
2
3
4
public class GoodsDTO {
private Goods goods;
private Category category;
}

2024-04-16 13:17:29
坨坨儿提问者 #3

已经解决了，谢谢！

2024-04-16 13:28:42