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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 • Feb 9

I solved everything in a single decorator now. For me it works fine. The objectMapper seems to be good in handling objects, however decoded json it seems not to understand in certain cases but this might improve in the near future.

decorator Thanks for rubberducking/pair programming this!

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.