cms-manage/app/model/customModel/Article.php

<?php
declare (strict_types = 1);

namespace app\model\customModel;

use app\model\Model;
use app\model\SubContent;

class Article extends Model
{
       public function subContent(): \think\model\relation\BelongsTo
       {
            return $this->belongsTo(SubContent::class,'sub_id','id');
       }

}