SpringBoot获取树状结构数据-SQL处理

前言

在开发中，层级数据（树状结构）的获取往往可能是我们一大难点，我现在将自己获取的树状结构数据方法总结如下,希望能给有需要的小伙伴有所帮助！

一、测试数据准备

/*
 Navicat Premium Data Transfer

 Source Server         : 本地MySQL-local
 Source Server Type    : MySQL
 Source Server Version : 80100
 Source Host           : localhost:33306
 Source Schema         : test

 Target Server Type    : MySQL
 Target Server Version : 80100
 File Encoding         : 65001

 Date: 06/09/2023 11:21:45
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for region
-- ----------------------------
DROP TABLE IF EXISTS `region`;
CREATE TABLE `region`  (
  `id` bigint(0) NOT NULL COMMENT '主键id',
  `region_id` bigint(0) NULL DEFAULT NULL COMMENT '区域id',
  `region_code` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '区域编码',
  `region_name` varchar(250) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '区域名称',
  `parent_id` bigint(0) NULL DEFAULT NULL COMMENT '父节点id',
  PRIMARY KEY (`id`) USING BTREE,
  UNIQUE INDEX `region_id`(`region_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin COMMENT = '地区信息' ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of region
-- ----------------------------
INSERT INTO `region` VALUES (1, 10001, 'CODEA0001', '中国', 0);
INSERT INTO `region` VALUES (2, 10002, 'CODEB0001', '安徽省', 10001);
INSERT INTO `region` VALUES (3, 10003, 'CODEB0002', '黑龙江省', 10001);
INSERT INTO `region` VALUES (4, 10004, 'CODEB0003', '广东省', 10001);
INSERT INTO `region` VALUES (5, 10005, 'CODEC0001', '合肥市', 10002);
INSERT INTO `region` VALUES (6, 10006, 'CODEC0002', '淮北市', 10002);
INSERT INTO `region` VALUES (7, 10007, 'CODEC0003', '哈尔滨市', 10003);
INSERT INTO `region` VALUES (8, 10008, 'CODEC0004', '鹤岗市', 10003);
INSERT INTO `region` VALUES (9, 10009, 'CODEC0005', '广州市', 10004);
INSERT INTO `region` VALUES (10, 10010, 'CODEC0006', '深圳市', 10004);
INSERT INTO `region` VALUES (11, 10011, 'CODED0001', '龙华区', 10010);
INSERT INTO `region` VALUES (12, 10012, 'CODED0002', '南山区', 10010);
INSERT INTO `region` VALUES (13, 10013, 'CODED0003', '天河区', 10009);

SET FOREIGN_KEY_CHECKS = 1;

二、对应表数据java实体类

import lombok.Data;
import java.util.List;

/**
 * @Project
 * @Description
 * @Author songwp
 * @Date 2023/9/5 15:16
 **/
@Data
public class Region{
    private Long id;
    private Long regionId;
    private String regionCode;
    private String regionName;
    private Long parentId;
    private List<Region> children;

}

三、对应mapper的调用方法

import com.songwp.pojo.entity.Region;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;

/**
 * @Project
 * @Description  在 持久层，我们只调用 getNodeTree 方法，parent_id = 0 代表顶级节点。然后通过 collection 节点继续调用 getNextNodeTree 方法进行循环调用。
 * @Author songwp
 * @Date 2023/9/5 15:22
 **/
@Mapper
public interface RegionMapper {

    List<Region> getNodeTree();
}

四、对应mapper.xml的写法（重点）

• column 代表会拿父节点 id ，作为参数获取 next 对象
• javaType 代表 next 对象是个列表，其实可以省略不写
• ofType 用来区分 JavaBean 属性类型和集合包含的类型
• select 是用来执行循环哪个 SQL

<?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="com.songwp.mapper.RegionMapper">

    <sql id="Base_Column_List">
        id,
        region_id,
        parent_id,
        region_code,
        region_name
    </sql>

    <resultMap id="BaseTreeResultMap" type="com.songwp.pojo.entity.Region">
        <result property="id" column="id" jdbcType="BIGINT"/>
        <result property="regionId" column="region_id" jdbcType="BIGINT"/>
        <result property="regionCode" column="region_code" jdbcType="VARCHAR"/>
        <result property="regionName" column="region_name" jdbcType="VARCHAR"/>
        <result property="parentId" column="parent_id" jdbcType="BIGINT"/>
        <collection column="region_id" property="children" javaType="java.util.ArrayList"
                    ofType="com.songwp.pojo.entity.Region" select="getNextNodeTree"/>
    </resultMap>

    <resultMap id="NextTreeResultMap" type="com.songwp.pojo.entity.Region">
        <result property="id" column="id" jdbcType="BIGINT"/>
        <result property="regionId" column="region_id" jdbcType="BIGINT"/>
        <result property="regionCode" column="region_code" jdbcType="VARCHAR"/>
        <result property="regionName" column="region_name" jdbcType="VARCHAR"/>
        <result property="parentId" column="parent_id" jdbcType="BIGINT"/>
        <collection column="region_id" property="children" javaType="java.util.ArrayList"
                    ofType="com.songwp.pojo.entity.Region" select="getNextNodeTree"/>
    </resultMap>

    <select id="getNextNodeTree" resultMap="NextTreeResultMap">
        SELECT
        <include refid="Base_Column_List"/>
        FROM region
        WHERE parent_id = #{id}
    </select>

    <select id="getNodeTree" resultMap="BaseTreeResultMap">
        SELECT
        <include refid="Base_Column_List"/>
        FROM region
        WHERE parent_id = 0000
    </select>
</mapper>

五、具体调用结果如下：

[
  {
    "id": 1,
    "regionId": 10001,
    "regionCode": "CODEA0001",
    "regionName": "中国",
    "parentId": 0,
    "children": [
      {
        "id": 2,
        "regionId": 10002,
        "regionCode": "CODEB0001",
        "regionName": "安徽省",
        "parentId": 10001,
        "children": [
          {
            "id": 5,
            "regionId": 10005,
            "regionCode": "CODEC0001",
            "regionName": "合肥市",
            "parentId": 10002,
            "children": []
          },
          {
            "id": 6,
            "regionId": 10006,
            "regionCode": "CODEC0002",
            "regionName": "淮北市",
            "parentId": 10002,
            "children": []
          }
        ]
      },
      {
        "id": 3,
        "regionId": 10003,
        "regionCode": "CODEB0002",
        "regionName": "黑龙江省",
        "parentId": 10001,
        "children": [
          {
            "id": 7,
            "regionId": 10007,
            "regionCode": "CODEC0003",
            "regionName": "哈尔滨市",
            "parentId": 10003,
            "children": []
          },
          {
            "id": 8,
            "regionId": 10008,
            "regionCode": "CODEC0004",
            "regionName": "鹤岗市",
            "parentId": 10003,
            "children": []
          }
        ]
      },
      {
        "id": 4,
        "regionId": 10004,
        "regionCode": "CODEB0003",
        "regionName": "广东省",
        "parentId": 10001,
        "children": [
          {
            "id": 9,
            "regionId": 10009,
            "regionCode": "CODEC0005",
            "regionName": "广州市",
            "parentId": 10004,
            "children": [
              {
                "id": 13,
                "regionId": 10013,
                "regionCode": "CODED0003",
                "regionName": "天河区",
                "parentId": 10009,
                "children": []
              }
            ]
          },
          {
            "id": 10,
            "regionId": 10010,
            "regionCode": "CODEC0006",
            "regionName": "深圳市",
            "parentId": 10004,
            "children": [
              {
                "id": 11,
                "regionId": 10011,
                "regionCode": "CODED0001",
                "regionName": "龙华区",
                "parentId": 10010,
                "children": []
              },
              {
                "id": 12,
                "regionId": 10012,
                "regionCode": "CODED0002",
                "regionName": "南山区",
                "parentId": 10010,
                "children": []
              }
            ]
          }
        ]
      }
    ]
  }
]