MyBatis实现三级树查询的示例代码

CREATE TABLE `sys_area` 
(  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键ID',
`parent_id` bigint(20) DEFAULT NULL COMMENT '父级ID', 
`name` varchar(50) NOT NULL COMMENT '地区名称',
`level` int(11) NOT NULL COMMENT '层级(1:省份 2:城市 3:区县)',
`sort` int(11) DEFAULT 0 COMMENT '排序号',  
`status` tinyint(4) DEFAULT 1 COMMENT '状态(0:禁用 1:启用)',  
`create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间', 
`update_time` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间', 
PRIMARY KEY (`id`),  
KEY `idx_parent_id` (`parent_id`)) 
ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='地区表';

@Data
public class Area implements Serializable {
      private static final long serialVersionUID = 1L;
          // 主键ID    
          private Long id;
          // 父级ID
          private Long parentId;
          // 地区名称
          private String name;
          // 层级   
          private Integer level; 
          // 排序号   
          private Integer sort;   
          // 状态   
          private Integer status;
          // 创建时间   
          private Date createTime;
          // 更新时间    
          private Date updateTime;  
          // 子节点列表   
          private List<Area> children;
      }

@Mapper
public interface AreaMapper {
    /**     
    * 查询所有地区数据    
    * @return 地区列表     */  
    List<Area> selectAllAreas(); 
    /**     
    * 根据父ID查询子地区     
    * @param parentId 父级ID     
    * @return 子地区列表     */   
    List<Area> selectAreasByParentId(Long parentId);        
    /**    
    * 查询指定层级的地区     
    * @param level 层级    
    * @return 地区列表     */  
    List<Area> selectAreasByLevel(Integer level);
}

<?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.example.mapper.AreaMapper">
    <!-- 基础列 -->  
    <sql id="Base_Column_List"> 
        id, parent_id, name, level, sort, status, create_time, update_time   
    </sql>       
    <!-- 查询所有地区 --> 
    <select id="selectAllAreas" resultType="com.example.entity.Area"> 
        SELECT   <include refid="Base_Column_List"/>    FROM sys_area 
        WHERE status = 1      
        ORDER BY sort ASC, id ASC   
    </select>       
    <!-- 根据父ID查询子地区 -->  
    <select id="selectAreasByParentId" resultType="com.example.entity.Area"> 
        SELECT     <include refid="Base_Column_List"/>     FROM sys_area        
        WHERE status = 1        
        AND parent_id = #{parentId}       
        ORDER BY sort ASC, id ASC   
    </select>      
    <!-- 查询指定层级的地区 -->   
    <select id="selectAreasByLevel" resultType="com.example.entity.Area">  
        SELECT     <include refid="Base_Column_List"/>    FROM sys_area        
        WHERE status = 1     
        AND level = #{level}    
        ORDER BY sort ASC, id ASC  
    </select>
</mapper>

@Service
@Slf4j
public class AreaServiceImpl implements AreaService {
    @Autowired
    private AreaMapper areaMapper; 
    @Override
    public List<Area> buildAreaTree() { 
        // 查询所有地区数据 
        List<Area> allAreas = areaMapper.selectAllAreas(); 
        // 构建树形结构
        return buildTree(allAreas);
    } 
    /**
    * 构建树形结构 
    * @param areas 地区列表 
    * @return 树形结构的地区列表 
    */ 
    private List<Area> buildTree(List<Area> areas) { 
        List<Area> trees = new ArrayList<>(); 
        // 获取所有根节点(省份)
        areas.stream().filter(area -> area.getLevel() == 1) .forEach(province -> { 
            // 设置省份的子节点(城市) 
            List<Area> cities = getChildren(areas, province.getId()); 
            province.setChildren(cities); 
            // 设置城市的子节点(区县)
            cities.forEach(city -> { List<Area> districts = getChildren(areas, city.getId());   
                city.setChildren(districts);  
            });
            trees.add(province);
        });
        return trees; 
    } 
    /**
    * 获取子节点 
    * @param areas 所有地区列表 
    * @param parentId 父级ID 
    * @return 子节点列表
    */ 
    private List<Area> getChildren(List<Area> areas, Long parentId) { 
        return areas.stream().filter(area -> Objects.equals(area.getParentId(), parentId)) 
        .collect(Collectors.toList()); 
    }
}

@RestController@RequestMapping("/api/areas")
public class AreaController {   
    @Autowired   
    private AreaService areaService;    
    /**    
    * 获取地区树形数据     */ 
    @GetMapping("/tree")   
    public ResponseResult<List<Area>> getAreaTree() { 
        try {       
            List<Area> trees = areaService.buildAreaTree();   
            return ResponseResult.success(trees);    
        } catch (Exception e) {   
            log.error("获取地区树形数据失败", e);    
            return ResponseResult.error("获取地区树形数据失败");     
        }  
   }
}

@Service
public class AreaServiceImpl implements AreaService {
    @Autowired   
    private RedisTemplate<String, List<Area>> redisTemplate; 
    private static final String AREA_TREE_KEY = "AREA:TREE";  
    private static final long CACHE_TIMEOUT = 24; 
    // 小时   
    @Override   
    public List<Area> buildAreaTree() {
        // 先从缓存获取  
        List<Area> cacheTree = redisTemplate.opsForValue().get(AREA_TREE_KEY);   
        if (cacheTree != null) {   
            return cacheTree;  
        }               
        // 缓存未命中，查询数据库并构建树    
        List<Area> trees = buildTreeFromDb();       
        // 放入缓存    
        redisTemplate.opsForValue().set(AREA_TREE_KEY, trees, CACHE_TIMEOUT, TimeUnit.HOURS);                return trees;
    }
}