以三级地区联动picker数据源为例

1，实体配置 以此类推 镇套村 村套屯 别忘了写get set

public class ADTownB {
    //镇编码
    private String value;
    //镇名称
    private String text;
   //村集合
   private List<AdCunB> children=new ArrayList<>();
}

2.SQL配置 collection 代表了嵌套的层级，里面的属性自行对应吧，picker每一级都是 value 和text，查询后系统会自动进行层级嵌套

   <resultMap id="townMap" type="com.common.entity.AdTownB">
        <id column="towncode" property="value" jdbcType="CHAR" />
        <result column="townname" property="text" jdbcType="NVARCHAR" />
        <collection property="children" ofType="com.common.entity.AdCunB">
            <id column="cuncode" property="value" jdbcType="CHAR" />
            <result column="cunname" property="text" jdbcType="NVARCHAR" />
            <collection property="children" ofType="com.common.entity.AdTunB">
                <id column="tuncode" property="value" jdbcType="CHAR" />
                <result column="tunname" property="text" jdbcType="NVARCHAR" />
            </collection>
        </collection>
    </resultMap>
    <!--获取三级镇村屯联动数据-->
    <select id="getThreelevelTown" resultMap="townMap" parameterType="java.lang.String">
        select tun.tuncode,tun.tunname,cun.cuncode,cun.cunname,town.towncode,town.townname             
        from AD_TUN_B tun
        left join AD_CUN_B cun on tun.cuncode=cun.cuncode
        left join AD_TOWN_B town on cun.towncode=town.towncode
    </select>

3.返回结果，用resultMap的类型接就可以，自动填充

List<AdTownB> list= commMapper.getThreelevelTown();