WitShop/app/Models/OrderItem.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

class OrderItem extends Model
{
    protected $fillable = ['order_id','product_variant_id','product_name','variant_label','quantity','unit_price','tax_rate'];

    protected $casts = ['unit_price' => 'decimal:2', 'tax_rate' => 'decimal:2'];

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

    public function variant(): BelongsTo
    {
        return $this->belongsTo(ProductVariant::class, 'product_variant_id');
    }

    public function getLineTotalAttribute(): float
    {
        return round($this->unit_price * $this->quantity, 2);
    }

    public function getTaxAmountAttribute(): float
    {
        $net = $this->unit_price / (1 + $this->tax_rate / 100);
        return round(($this->unit_price - $net) * $this->quantity, 2);
    }
}