Implementing Custom Eloquent Casts for Value Objects

<?php
// 1. Create a Value Object (e.g., app/ValueObjects/Money.php)
namespace App\ValueObjects;

use InvalidArgumentException;

class Money
{
    public function __construct(
        public float $amount,
        public string $currency = 'USD'
    ) {
        if ($amount < 0) {
            throw new InvalidArgumentException("Amount cannot be negative.");
        }
    }

    public function formatted(): string
    {
        return $this->currency . ' ' . number_format($this->amount, 2);
    }

    public function equals(Money $other): bool
    {
        return $this->amount === $other->amount && $this->currency === $other->currency;
    }
}

// 2. Create a Custom Cast Class (e.g., app/Casts/MoneyCast.php)
namespace App\Casts;

use App\ValueObjects\Money;
use Illuminate\Contracts\Database\Eloquent\CastsAttributes;
use Illuminate\Database\Eloquent\Model;

class MoneyCast implements CastsAttributes
{
    public function get(Model $model, string $key, mixed $value, array $attributes): mixed
    {
        // Assuming the database stores the amount as a float/decimal
        // and currency might be in another column or fixed.
        // For simplicity, we'll assume 'price' column stores amount.
        // If currency is also dynamic, it would be passed via $attributes.
        return new Money((float) $value, $attributes['currency'] ?? 'USD');
    }

    public function set(Model $model, string $key, mixed $value, array $attributes): mixed
    {
        if (!$value instanceof Money) {
            throw new InvalidArgumentException('The given value is not a Money instance.');
        }

        // When saving, store just the amount (float) in the 'price' column.
        // If currency was dynamic, you'd set that too.
        return $value->amount;
    }
}

// 3. Use the Custom Cast in your Eloquent Model (e.g., app/Models/Product.php)
namespace App\Models;

use App\Casts\MoneyCast; // Don't forget to import
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Product extends Model
{
    use HasFactory;

    protected $fillable = ['name', 'price', 'currency'];

    protected $casts = [
        'price' => MoneyCast::class, // Apply the custom cast
    ];
}

// Example Usage in a controller or route
use App\Models\Product;
use App\ValueObjects\Money;

// Create a product
$product = Product::create([
    'name' => 'Fancy Gadget',
    'price' => 99.99, // Stored as float, cast to Money on retrieval
    'currency' => 'EUR',
]);

// Retrieve and interact with the Money object
$retrievedProduct = Product::find($product->id);
echo $retrievedProduct->price->formatted(); // Output: EUR 99.99

// Update the product's price using a Money object
$retrievedProduct->price = new Money(120.50, 'GBP');
$retrievedProduct->save(); // Mutator handles saving just the amount

$updatedProduct = Product::find($product->id);
echo $updatedProduct->price->formatted(); // Output: GBP 120.50 (if currency column was updated too)