二级分类菜单及三级分类菜单的层级结构返回

前言

在开发投诉分类功能模块时，遇到过这样一个业务场景：后端需要按层级结构返回二级分类菜单所需数据，换言之，将具有父子关系的List结果集数据转为树状结构数据来返回

二级分类菜单

前期准备

这里简单复刻下真实场景中出现的二级分类菜单层级结构返回

数据库设计

建表语句如下

DROP TABLE IF EXISTS `menu`;
CREATE TABLE `menu`  (`id` bigint NOT NULL AUTO_INCREMENT,`name` varchar(50) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL COMMENT '名称',`parent_id` bigint NULL DEFAULT NULL COMMENT '父级id',PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci ROW_FORMAT = DYNAMIC;-- ----------------------------
-- Records of menu
-- ----------------------------
INSERT INTO `menu` VALUES (1, '质量问题', 0);
INSERT INTO `menu` VALUES (2, '变质', 1);
INSERT INTO `menu` VALUES (3, '过期', 1);
INSERT INTO `menu` VALUES (4, '包装破损', 1);
INSERT INTO `menu` VALUES (5, '服务问题', 0);
INSERT INTO `menu` VALUES (6, '态度恶劣', 5);
INSERT INTO `menu` VALUES (7, '东拉西扯', 5);

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效果图预览

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这里是在SpringBoot项目中演示实现的，持久层框架选用MyBatis-Plus，版本号：3.5.3.1

🌟之所以强调MP版本号，是因为之前在实现分页时遇过挫，真实项目选用的版本是3.3.2，而自己在学习MP时，选择版本是3.5.3.1。MP官方文档在不同版本中，有关分页插件的使用介绍可能存在不同，实际开发中对引入MP依赖的版本号还是要有所关注

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开发测试

创建实体类

package com.atguigu.mybatisplus.pojo;import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;/*** @author Songguo* @date 2023/11/15 9:56*/
@Data
@TableName("menu")
public class Menu {private Long id;private String name;private Long parentId;
}

创建mapper层

package com.atguigu.mybatisplus.mapper;import com.atguigu.mybatisplus.pojo.Menu;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;public interface MenuMapper extends BaseMapper<Menu> {
}

创建service层接口及实现类

package com.atguigu.mybatisplus.service;import com.atguigu.mybatisplus.pojo.Menu;
import com.baomidou.mybatisplus.extension.service.IService;public interface MenuService extends IService<Menu> {
}

package com.atguigu.mybatisplus.service.impl;import com.atguigu.mybatisplus.mapper.MenuMapper;
import com.atguigu.mybatisplus.pojo.Menu;
import com.atguigu.mybatisplus.service.MenuService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;/*** @author Songguo* @date 2023/11/15 10:00*/
@Service
public class MenuServiceImpl extends ServiceImpl<MenuMapper, Menu> implements MenuService {
}

创建测试类

package com.atguigu.mybatisplus;import com.atguigu.mybatisplus.pojo.Menu;
import com.atguigu.mybatisplus.service.MenuService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;/*** @author Songguo* @date 2023/11/15 10:02*/
@SpringBootTest
public class MenuServiceImplTest {@Autowiredprivate MenuService menuService;@Testpublic void ListToTreeTest() {List<Menu> list = menuService.list();// 存放要返回的树状结构数据List<Map<String, Object>> MenuList = new ArrayList<>();for (Menu menu : list) {if (Long.valueOf(0) == menu.getParentId()) {Map<String, Object> map = new HashMap<>();map.put("id", menu.getId());map.put("name", menu.getName());// map.put("parentId", menu.getParentId());map.put("children", getChildren(list, menu.getId()));MenuList.add(map);}}MenuList.forEach(System.out::println);}public List<Map<String, Object>> getChildren(List<Menu> list, Long topId) {List<Map<String, Object>> data = new ArrayList<>();for (Menu menu : list) {if (topId == menu.getParentId()) {Map<String, Object> map = new HashMap<>();map.put("id", menu.getId());map.put("name", menu.getName());// map.put("parentId", menu.getParentId());data.add(map);}}return data;}}

注意： 在真实场景中，并不需要返回每条记录的所有字段值，主要看前端需要接收那些数据

实现思路很简单：

1️⃣获取分类菜单所有记录

2️⃣遍历找出一级节点（父节点），然后在调用getChildren()（重金寻子方法）获取二级节点（子节点）

3️⃣通过List<Map<String,Object>>来存放结果集

三级分类菜单

前期准备

这里简单复刻下真实场景中出现的三级分类菜单层级结构返回

数据库设计

建表语句如下

CREATE TABLE address (id INT AUTO_INCREMENT PRIMARY KEY,name VARCHAR(50) NOT NULL,parent_id INT NOT NULL,level INT NOT NULL
);INSERT INTO address (name, parent_id, level) VALUES ('湖北', 0, 1);
INSERT INTO address (name, parent_id, level) VALUES ('辽宁', 0, 1);
INSERT INTO address (name, parent_id, level) VALUES ('武汉', 1, 2);
INSERT INTO address (name, parent_id, level) VALUES ('荆州', 1, 2);
INSERT INTO address (name, parent_id, level) VALUES ('沈阳', 2, 2);
INSERT INTO address (name, parent_id, level) VALUES ('蔡甸区', 3, 3);
INSERT INTO address (name, parent_id, level) VALUES ('江夏区', 3, 3);
INSERT INTO address (name, parent_id, level) VALUES ('沙市区', 4, 3);
INSERT INTO address (name, parent_id, level) VALUES ('大东区', 5, 3);
INSERT INTO address (name, parent_id, level) VALUES ('浑南区', 5, 3);

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效果图预览

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开发测试

创建实体类

package com.atguigu.mybatisplus.pojo;import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;/*** @author Songguo* @date 2023/11/26 17:04*/
@Data
@TableName("address")
public class Address {private int id;private String name;private int parentId;private int level;
}

创建mapper层

package com.atguigu.mybatisplus.mapper;import com.atguigu.mybatisplus.pojo.Address;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;public interface AddressMapper extends BaseMapper<Address> {
}

创建service层接口及实现类

package com.atguigu.mybatisplus.service;import com.atguigu.mybatisplus.pojo.Address;
import com.baomidou.mybatisplus.extension.service.IService;public interface AddressService extends IService<Address> {
}

package com.atguigu.mybatisplus.service.impl;import com.atguigu.mybatisplus.mapper.AddressMapper;
import com.atguigu.mybatisplus.pojo.Address;
import com.atguigu.mybatisplus.service.AddressService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;/*** @author Songguo* @date 2023/11/26 17:08*/
@Service
public class AddressServiceImpl extends ServiceImpl<AddressMapper, Address> implements AddressService {
}

创建测试类

package com.atguigu.mybatisplus;import com.atguigu.mybatisplus.pojo.Address;
import com.atguigu.mybatisplus.service.AddressService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;/*** @author Songguo* @date 2023/11/26 17:10*/
@SpringBootTest
public class AddressServiceImplTest {@Autowiredprivate AddressService addressService;@Testpublic void getAddress() {List<Address> list = addressService.list();// list.forEach(System.out::println);// 存放结果集List<Map<String, Object>> addressList = new ArrayList<>();for (Address address : list) {if (address.getLevel() == 1) {Map<String, Object> map = new HashMap<>();map.put("id", address.getId());map.put("name", address.getName());// map.put("parentId", address.getParentId());map.put("children", getChildren(list, address.getId()));addressList.add(map);}}addressList.forEach(System.out::println);}public List<Map<String, Object>> getChildren(List<Address> list, int parentId) {List<Map<String, Object>> data = new ArrayList<>();for (Address address : list) {HashMap<String, Object> map = new HashMap<>();if (parentId == address.getParentId()) {map.put("id", address.getId());map.put("name", address.getName());// map.put("parentId", address.getParentId());if (address.getLevel() < 3) {map.put("children", getChildren(list, address.getId()));}data.add(map);}}return data;}}