warehouse/app/Models/Stock.php

<?php

namespace App\Models;

use Framework\Database\Model;

class Stock extends Model
{
    protected string $table = 'stock';

    public function item(): mixed
    {
        return $this->belongsTo(Item::class, 'item_id');
    }

    public function location(): mixed
    {
        return $this->belongsTo(Location::class, 'location_id');
    }

    public static function forItemAtLocation(int $itemId, int $locationId): static
    {
        $stock = static::where('item_id', $itemId)->where('location_id', $locationId)->first();

        if ($stock) {
            return $stock;
        }

        $stock = new static();
        $stock->item_id = $itemId;
        $stock->location_id = $locationId;
        $stock->quantity = 0;

        return $stock;
    }
}