class Article extends Model{
   public function category()
    {
        return $this->belongsToMany('App\Categorys', 'relations', 'term_taxonomy_id', 'object_id');
    }
}

$res = Article::with('category')->where('id', $id)->get();

参考：https://segmentfault.com/q/10...，使用with

RTFMhttps://laravel-china.org/doc...