获取子栏目的方法应该放在Entity层还是Service层？

package com.test.blog.pojo.po;

import java.util.List;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.activerecord.Model;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * 栏目实体类
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Cat extends Model<Cat> {
    @TableId(type = IdType.AUTO)
    private Integer catid;
    private String catname;
    private Integer pid;
    private String title;
    private String description;
    private Integer sortid;
    private Short pagesize;

    public List<Cat> getChildren() {
        QueryWrapper<Cat> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("pid", this.catid);
        List<Cat> list = this.selectList(queryWrapper); // 注意这里调用了this.selectList
        return list;
    }
}