当返回前端的数据中存在List对象集合，如何优雅操作？

爱被打了一巴掌 2022-10-09 03:27 114阅读 0赞

### 文章目录 ###

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

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# 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 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>
    
    
        <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);
    }

--------------------

欢迎一键三连~  
  
有问题请留言，大家一起探讨学习  
  
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