weixin/app/Repositories/Models/Exam/Paper.php

<?php

namespace App\Repositories\Models\Exam;

use App\Repositories\Models\Mentor\Grade;
use App\Repositories\Models\Model;

class Paper extends Model
{
    /**
     * @var string
     */
    protected $table = 'exam_papers';

    protected $guarded = [];

    protected $casts = [
        'banks' => 'json'
    ];

    /**
     * The attributes excluded from the model's JSON form.
     *
     * @var array
     */
    protected $hidden = [];

    public function models()
    {
        return $this->belongsToMany(Grade::class, PaperModel::class, 'paper_id', 'model_id')->select(['mentor_grades.id', 'mentor_grades.name']);
    }

//    public function banks()
//    {
//        return $this->belongsToMany(Bank::class, PaperBank::class);
//    }

    public function records()
    {
        return $this->hasMany(Record::class, 'paper_id');
    }

}