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

<?php

namespace App\Repositories\Models\Exam;

use App\Repositories\Models\Model;

class Bank extends Model
{
    /**
     * @var string
     */
    protected $table = 'exam_banks';

    protected $guarded = [];

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

    public function category()
    {
        return $this->belongsTo(BankCategory::class, 'category_id')->select(['id', 'name']);
    }
}