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Level Up Your DTOs: Pro Techniques for the Symfony ObjectMapper

Matt Mochalkin on October 18, 2025

We often reach for tools that solve immediate problems. When it comes to hydrating objects from raw data, many of us see the ObjectMapper component...

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arthurGrinjo • Feb 3

And another issue popped up; I'm trying to map an array of objects.

Documentation states: (documentation)

However I'm not able to make this happen, did you?

Matt Mochalkin • Feb 3

Weekend project for me) Turning this article into a GitHub repo.

arthurGrinjo • Feb 4 • Edited

I started a new repo with some test-commands. Test 1, 2, 4 are working, 3 fails, 5 I still have to build. Test 6 probably is a test for trying to fix the name-converter without a decorator. (or maybe perhaps with an decorator)

repo

Matt Mochalkin • Feb 6

It's done) github.com/mattleads/SymfonyObject...

arthurGrinjo • Feb 6

Nice! Will have a closer look at it this weekend. But already love the nested object implementation. The posts are not converted into objects, not sure if the transformer is actually triggered.

Matt Mochalkin • Feb 6

Updated. Check once more.

arthurGrinjo • Jan 28 • Edited

Hi @mattleads ,

I tried to use the snake_case to CamelCase converter in Symfony 8.0 but I'm not able to make it work. You already tried this? Only way I get to function snake_case combined with CamelCase is by using the

#[Map(source: 'snake_case')] public string $snakeCase,

Thanks in advance! Regards Arthur

Matt Mochalkin • Jan 28

All works fine)) Clean Symfony 8.0 installed just for you))

class ApiUserDto
{
    public function __construct(
        #[Map(source: 'user_id')]
        public int $userId,
        #[Map(source: 'first_name')]
        public string $firstName,
        #[Map(source: 'last_name')]
        public string $lastName
    ) {}
}

        $data = [
            'user_id' => 99,
            'first_name' => 'Jane',
            'last_name' => 'Doe'
        ];

        var_dump($data);

        $apiUser = $this->objectMapper->map((object)$data, ApiUserDto::class);

        var_dump($apiUser);

array(3) {
  ["user_id"]=>
  int(99)
  ["first_name"]=>
  string(4) "Jane"
  ["last_name"]=>
  string(3) "Doe"
}
object(App\DTO\ApiUserDto)#3171 (3) {
  ["userId"]=>
  int(99)
  ["firstName"]=>
  string(4) "Jane"
  ["lastName"]=>
  string(3) "Doe"
}

arthurGrinjo • Jan 29 • Edited

Thanks for your effort! Sorry for the confusion.. That actually works great and that's the way I'm doing it right now. However, I'm trying to implement this name-converter:

serializer.name_converter.snake_case_to_camel_case

And I can't get it to work.. Not sure what I'm missing.. Probably it moved to another location (config/packages/serializer.yaml) but that's in my opinion about serializing and not about object mapping.. So I'm a little confused.

But when I get this name-converter to work that will save me a great amount of time :)

Matt Mochalkin • Jan 29

I'd suggest to use Decorator))

namespace App\ObjectMapper;

use Symfony\Component\DependencyInjection\Attribute\AsDecorator;
use Symfony\Component\ObjectMapper\ObjectMapperInterface;

#[AsDecorator(decorates: ObjectMapperInterface::class)]
readonly class SnakeCaseDecorator implements ObjectMapperInterface
{
    public function __construct(
        private ObjectMapperInterface $innerMapper
    ) {}

    public function map(object|array $source, object|string|null $target = null, array $context = []): object
    {
        if (is_array($source)) {
            if (!($context['skip_normalization'] ?? false)) {
                $source = $this->convertKeysToCamelCase($source);
            }
            $source = (object) $source;
        }

        return $this->innerMapper->map($source, $target, $context);
    }

    private function convertKeysToCamelCase(array $data): array
    {
        $result = [];
        foreach ($data as $key => $value) {
            if (is_array($value)) {
                $value = $this->convertKeysToCamelCase($value);
            }

            $newKey = lcfirst(str_replace('_', '', ucwords($key, '_')));

            $result[$newKey] = $value;
        }

        return $result;
    }
}

And no more #Map needed))

arthurGrinjo • Jan 29 • Edited

Yeah that's also a good option! But that draws me to the conclusion that this configuration via the framework.yaml file with the name_converter isn't working as we expected. Because I would love the implementation. And I tried it in the serializer.yaml file but that also didn't work out.

arthurGrinjo • Jul 16

So a few months later, I still could not let this rest.. And found the real solution without any code: api-platform.com/docs/v3.4/core/se... :)

arthurGrinjo • Jul 30

Back again. I thought I had some working code, also for relations. However I made an mistake with git repos and lost track... How would you suggest to handle IRI's in the DTO structure?

I thought ApiPlatform deserialization already included IRI to object conversion. However my code doesn't seem to understand this.

###ActivityApiResource
#[ApiResource(
    shortName: 'Activity',
    stateOptions: new Options(entityClass: ActivityEntity::class),
)]
#[Post(
    uriTemplate: '/activitities'
    input: ActivityRequestDto::class,
    output: ActivityResponseDto::class,
    processor: Processor::class,
    //map: false, /** default true -> forces RequestDto to execute IriToObject */
)]

###ActivityRequestDto.php
#[Map(target: Comment::class)]
class ActivityRequestDto implements RequestDto
{
    #[Assert\Length(min: 3, max: 1024)]
    public string $activity;

    #[Assert\Regex(RegexValidations::IRI)]
    #[Map(transform: [IriToObject::class])]
    public string $user;
}

###IriToObject.php
public function __invoke(
    mixed $value,
    object $source,
    ?object $target,
): object {
    return (is_string($value))
        ? $this->iriConverter->getResourceFromIri($value)
        : throw new Exception('Unable to convert IRI into object')
    ;
}

However getResourceFromIri does not return the object. It returns the UserResponseDto which ofcourse is not part of the relation. That's the User entity. So mapper concludes:

Expected argument of type "App\Entity\User", \"App\Dto\User\Response\UserResponseDto" given at property path "user".

I could improve the IriToObject script. However would love to rely on ApiPlatform logic...