Tree structure entity class:

@data 
 @Equalsandhashcode (callsuper = false) 
 @Accessors (chain = true) 
 @Tablename ("Area_info") 
 public class areainfo { 
 // Administrative area number 
     @Tableid (value = "Area_no", Type = IDType.id_Worker_Str) 
 Private String Areano; 
 // Administrative area name 
     @Tablefield ("Area_name") 
 Private String Areaname; 
 // Father Area Number 
     @Tablefield ("Parent_area_no") 
 Private String Parentareano; 
     // Remark 
     @Tablefield ("Remark") 
 Private String Remark; 
 // Status (0-invalid; 1-valid) 
     @Tablefield ("STATUS") 
 Private String Status; 
     // child elements 
     @Tablefield (exist = false) 
 Private list <MCSAREAINFO> Children; 
 }

database table mechanism is as follows:

Create table `rea_info` ( 
   `rea_no` varchar (32) not null comments 'administrative area number', 
   `rea_name` varchar (128) default null comment 'administrative area name', 
   `Parent_area_no` varchar (32) default null comments 
   `Remark` varchar (512) default null comments 'remarks', 
   `Status` varchar (8) default null comments (0-invalid; 1-valid) ',, valid)', 
   Primary Key (`rea_no`) 
 ) ENGINE = Innodb Default Charset = UTF8 Comment = 'Area Table';

java dao is as follows:

@mapper 
 Public Interface Areainfodao Extends Basemapper <reainfo> { 
 // Get the area tree menu 
 Public list <reainfo> getareainfotree (String Parentareano); 
 }

mybatis SQL as follows:

<resultMap type="com.AreaInfo" id="areaInfoResult">
        <id column="AREA_NO" property="areaNo"/>
        <result column="AREA_NAME" property="areaName"/>
        <result column="STATUS" property="status"/>
        <collection column="AREA_NO" property="children" ofType="com.AreaInfo"                 
        select="getAreaInfoTree"></collection>     </resultMap>
 <select id="getAreaInfoTree" resultMap="areaInfoResult" parameterType="string">
        select AREA_NO,AREA_NAME,PARENT_AREA_NO,STATUS from AREA_INFO where             
        PARENT_AREA_NO=#{parentAreaNo}
 </select>

Instructions:This query method is only suitable for a small amount of data query. If the amount of data is too large, the pressure of the database is particularly large, so it is not recommended to use it. For a large amount of tree data, you can use a lazy loading method or directly query the list and hand it over to the previous paragraph to the previous paragraph. Do it yourself.