List 集合，如何优雅地返回给前端？

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sceneListofType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);

}