Symfony 7 Map nested request data

Question

I'm trying to map and validate using #[MapRequestPayload] request payload with nested request data. When I want to map request with just 1 question, everything works fine, but when I switch type of the $question property in Quiz DTO I get this validation error.

CreateQuizDto.php

class CreateQuizDto
{
    #[Assert\NotBlank()]
    #[Assert\Length(min: 1, max: 255)]
    public string $label;

    #[Assert\Type('countable')]
    #[Assert\All(new Assert\Type(CreateQuestionDto::class))]
    #[Assert\Valid]
    public array $questions;
}

CreateQuestionDto.php

class CreateQuestionDto
{
    #[Assert\NotBlank()]
    #[Assert\Length(min: 1, max: 255)]
    public string $label;
}

Controller.php

#[Route('/api', format: 'json')]
class QuizController extends AbstractController
{
    #[Route('/quiz', name: 'app_quiz', methods: ['POST'])]
    public function index(#[MapRequestPayload] CreateQuizDto $dto): JsonResponse
    {
        return $this->json([
            'dto' => $dto

        ]);
    }
}

Example request body

{
  "label": "Example Quiz",
  "questions": [
    {
      "label": "Example Question 1"
    },
    {
      "label": "Example Question 2"
    }
  ]
}

Response error

{
 "type": "https://symfony.com/errors/validation",
    "title": "Validation Failed",
    "status": 422,
    "detail": "questions[0]: This value should be of type App\\Dto\\CreateQuestionDto.\nquestions[1]: This value should be of type App\\Dto\\CreateQuestionDto.",
    "violations": [
        {
            "propertyPath": "questions[0]",
            "title": "This value should be of type App\\Dto\\CreateQuestionDto.",
            "template": "This value should be of type {{ type }}.",
            "parameters": {
                "{{ value }}": "array",
                "{{ type }}": "App\\Dto\\CreateQuestionDto"
            },
            "type": "urn:uuid:ba785a8c-82cb-4283-967c-3cf342181b40"
        },
        {
            "propertyPath": "questions[1]",
            "title": "This value should be of type App\\Dto\\CreateQuestionDto.",
            "template": "This value should be of type {{ type }}.",
            "parameters": {
                "{{ value }}": "array",
                "{{ type }}": "App\\Dto\\CreateQuestionDto"
            },
            "type": "urn:uuid:ba785a8c-82cb-4283-967c-3cf342181b40"
        }
    ],
}

Answer 1

The problem here is that Symfony doesn't know that your public array $questions; has type array<CreateQuestionDto> as PHP for now doesn't use generics. So to explicitly "set the type" in deserialization process you should use constructor:

class CreateQuizDto
{
// ...
    public function __construct(string $label, array $questions)
    {
        $this->label = $label;

        // Map the array of questions to CreateQuestionDto objects
        $this->questions = array_map(
            fn ($question) => new CreateQuestionDto($question['label']),
            $questions
        );
    }
}

And add constructor to CreateQuestionDto:

public function __construct(string $label)
{
    $this->label = $label;
}

Using constructors in DTO makes your life easier 😉