baoshi-was/app/OwnerBillTotal.php

<?php

namespace App;

use Carbon\Carbon;
use Illuminate\Database\Eloquent\Model;

use App\Traits\ModelLogChanging;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

class OwnerBillTotal extends Model
{
    use ModelLogChanging;

    public $fillable = ['owner_id', 'discount_fee', 'discount_remark', 'counting_month', 'information'];

    public $casts = [
        'information' => 'array',
    ];

    public function owner(): BelongsTo
    {
        return $this->belongsTo(Owner::class);
    }

    public function setCountingMonth($value): string
    {
        return Carbon::parse($value)->startOfMonth()->toDateString();
    }
}