Symfony Validation

You are an expert in multi-layer validation within Symfony hexagonal architecture.

When to Activate

• User needs input validation
• User asks about validation strategies
• User needs custom constraints
• User mentions DTO validation or domain invariants

Version Notes

Feature	Requires	Fallback
#[MapRequestPayload] / #[MapQueryString] auto-validation	Symfony 6.3	manual ValidatorInterface::validate()
Named-argument constraints Length(min: 2)	all versions; arrays removed in 8.0	-
Custom constraint with named-argument constructor	required for 8.0 (arrays deprecated 7.3)	same code works on 6.4
#[ExtendsValidationFor(Target::class)]	Symfony 7.4	validate a Request DTO / Command instead
When(..., otherwise: [...])	Symfony 7.3	two constraints with groups

3-Layer Validation Strategy

Layer 1: Presentation (Input Validation)

Where: Request DTOs in Presentation/{Module}/API/Request/ What: Format validation: is the input well-formed? How: Constraints on the DTO + #[MapRequestPayload] (422 on failure)

namespace App\Presentation\User\API\Request;

use Symfony\Component\Validator\Constraints as Assert;

final readonly class RegisterUserRequest
{
    public function __construct(
        #[Assert\NotBlank]
        #[Assert\Email]
        public string $email = '',

        #[Assert\NotBlank]
        #[Assert\Length(min: 2, max: 100)]
        public string $name = '',

        #[Assert\NotBlank]
        #[Assert\Length(min: 8)]
        #[Assert\Regex(pattern: '/[A-Z]/', message: 'Must contain uppercase')]
        #[Assert\Regex(pattern: '/[0-9]/', message: 'Must contain a number')]
        public string $password = '',
    ) {
    }
}

// Controller
public function register(#[MapRequestPayload] RegisterUserRequest $request): JsonResponse

Layer 2: Application (Command Validation)

Where: Command/Query classes, validated by the Messenger validation middleware What: Use-case pre-checks: are the values acceptable for this use case (including checks that need ports, e.g. uniqueness)? How: Symfony Validator constraints on command properties

final readonly class RegisterUser
{
    public function __construct(
        #[Assert\NotBlank]
        #[Assert\Email]
        #[UniqueEmail]
        public string $email,

        #[Assert\NotBlank]
        public string $name,

        #[Assert\NotBlank]
        public string $plainPassword,
    ) {
    }
}

The validation middleware validates before handler execution and throws Messenger\Exception\ValidationFailedException (mapped to 422 by ApiExceptionSubscriber). Commands dispatched from CLI, Scheduler or other handlers are validated too, which is why this layer exists even with Layer 1.

Layer 3: Domain (Invariants)

Where: Entity constructors/factories, value objects, business methods What: Business invariants: is the operation valid in domain context? How: Pure PHP checks, throw domain exceptions (no #[Assert] attributes in Domain)

// Value object self-validates
final readonly class Email
{
    public function __construct(public string $value)
    {
        if (filter_var($value, FILTER_VALIDATE_EMAIL) === false) {
            throw InvalidEmailException::forValue($value);
        }
    }
}

// Entity protects invariants
final class Order
{
    public function cancel(string $reason, \DateTimeImmutable $now): void
    {
        if (!$this->status->canTransitionTo(OrderStatus::CANCELLED)) {
            throw InvalidOrderTransitionException::from($this->id->value, $this->status, OrderStatus::CANCELLED);
        }
        // ...
    }
}

References

See references/ for detailed guides:

• validation-layers.md - Full examples for each layer, custom constraints, #[ExtendsValidationFor], groups, pre-6.3 fallback