baoshi-was/app/PaperBox.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class PaperBox extends Model
{
    protected $fillable=[
        'model','length','width','height',
    ];

    public function owners(){
        return $this->belongsToMany('\App\Owner','owner_paper_box','paper_box_id','owner_id');
    }
}