Custom Rules

Implement Antares\Validation\Attributes\ValidationAttribute to create a custom rule:

use Antares\Validation\Attributes\ValidationAttribute;
use Attribute;

#[Attribute(Attribute::TARGET_PARAMETER)]
final class Slug implements ValidationAttribute
{
    public function validate(mixed $value): ?string
    {
        if (!preg_match('/^[a-z0-9]+(?:-[a-z0-9]+)*$/', (string) $value)) {
            return 'Must be a valid slug.';
        }

        return null;
    }
}

Return a string error message if validation fails, null if it passes. Then use it like any built-in attribute:

#[Dto]
readonly class CreatePostRequest
{
    public function __construct(
        #[NotBlank]
        public string $title,

        #[NotBlank]
        #[Slug]
        public string $slug,
    ) {}
}

Parameterised Rules

Custom attributes can accept constructor arguments:

#[Attribute(Attribute::TARGET_PARAMETER)]
final class StartsWith implements ValidationAttribute
{
    public function __construct(private readonly string $prefix) {}

    public function validate(mixed $value): ?string
    {
        if (!str_starts_with((string) $value, $this->prefix)) {
            return "Must start with \"{$this->prefix}\".";
        }

        return null;
    }
}

#[StartsWith('SKU-')]
public string $sku,