account_book/app/Models/Merchant.php

<?php

namespace App\Models;

use Dcat\Admin\Traits\HasDateTimeFormatter;
use Illuminate\Database\Eloquent\Model;

class Merchant extends Model
{
    use HasDateTimeFormatter;

    public static function getAllMerchant(): array
    {
        $merchants = self::all();

        $list = [];

        foreach ($merchants as $merchant) {
            $list[$merchant->mch_no] = "[$merchant->mch_no]$merchant->mch_name";
        }

        return $list;
    }
}