• 1.业务背景
• 2.实体类
• 3.自定义MApper和xml文件
• 4.Service层
• 5.Controller层

1.业务背景

业务场景中，一个会话中存在多个场景，即一个session_id对应多个scene_id和scene_name

如果你写成如下的聚合模型类

public class SceneVO {
 private String sessionId;
 private String sceneId;
 private String sceneName;
 // 省略对应的getter和setter方法
}

返回的List<SceneVO>形式如下，这个数据在data属性中

{
 "data":[
  {
   "sessionId": "jksadhjksd",
   "sceneId":"NDJWKSDSJKDKED",
   "sceneName":"场景1"
  },
  {
   "sessionId": "jksadhjksd",
   "sceneId":"KLJSDJKLSDFALK",
   "sceneName":"场景2"
  },
  {
   "sessionId": "jksadhjksd",
   "sceneId":"KERFJKOVDJKDSS",
   "sceneName":"场景3"
  }
 ]
}

每个对象里面都带上了重复的一个sessionId数据，我想提出来该怎么办？

我想改为如下形式，sessionId提出到外层，更能体现出一个sessionId对应多个sceneId和sceneName的含义，这样也便于前端取数据，不然每个对象都要增加一个sessionId属性，太麻烦。

{
 "data": {
  "sessionId": "jksadhjksd",
  "sceneList": [
   {
    "sceneId":"NDJWKSDSJKDKED",
    "sceneName":"场景1"
   },
   {
    "sceneId":"KLJSDJKLSDFALK",
    "sceneName":"场景2"
   },
   {
    "sceneId":"KERFJKOVDJKDSS",
    "sceneName":"场景3"
   }
  ]
 }
}

2.实体类

方法如下，首先创建两个实体类。

public class SceneVO {
 private String sessionId;
 private List<SubSceneVO> sceneList;
 // 省略对应的getter和setter方法
}
public class SubSceneVO {
 private String sceneId;
 private String sceneName;
 // 省略对应的getter和setter方法
}

3.自定义Mapper和xml文件

public interface BusinessScenesCustomMapper {
 SceneVO selectBySessionId(String sessionId);
}
<?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="你的包名.mapper.BusinessScenesCustomMapper">
    <resultMap id="BaseResultMap" type="你的包名.vo.SceneVO">
        <result column="session_id" jdbcType="VARCHAR" property="sessionId"/>
    <!--
      collection 标签：用于定义关联的list集合类型的封装规则
      property：对应父类中list属性名，这里SceneVO类里的List变量名为sceneList
      ofType：集合存放的类型，List集合要装的类的类名，这里是SubSceneVO
    -->
        <collection property="sceneList" ofType="你的包名.vo.SubSceneVO">
            <result column="scene_id" jdbcType="VARCHAR" property="sceneId"/>
            <result column="scene_name" jdbcType="VARCHAR" property="sceneName"/>
        </collection>
    </resultMap>

<!-- 一个session_id对应多条记录，返回的是SceneVO对象，SceneVO对象有一个List装着SubSceneVO  -->
    <select id="selectBySessionId" parameterType="string" resultMap="BaseResultMap">
        select session_id, scene_id, scene_name
        from 表名
        where session_id = #{sessionId,jdbcType=VARCHAR}
    </select>
</mapper>

• collection标签： 用于定义关联的List集合类型的封装规则
• property属性： 对应父类中List集合的变量名，这里SceneVO类里的List变量名为sceneList
• ofType属性： 集合存放的类型，List集合要装的类的类名，这里是SubSceneVO

4.Service层

public interface SceneService {
 /**
 * 获取场景信息
 */
 SceneVO getScenesInfo(String sessionId);
}
@Service
public class SceneServiceImpl {

 @Resource
 private BusinessScenesCustomMapper businessScenesCustomMapper;
 ......
 public SceneVO getScenesInfo(String sessionId) {
  return businessScenesCustomMapper.selectBySessionId(sessionId);
 }
}

5.Controller层

......
@Resource
private SceneService sceneService;

@GetMapping("/getScenesInfo")
public ResModel getScenesInfo(String sessionId) {
 SceneVO sceneVO = sceneService.getScenesInfo(sessionId);
 return ResModel.ok(sceneVO);
}

原文链接：
https://mp.weixin.qq.com/s/lbppT1VSAUN06L3MTTDmJg