How to serialize object as its own property (array) using JMS Serializer EventSubscriberInterface (php, symfony)

I need to serialize an object as its own property (it’s type is array), I mean that the object has an array property books, and after transforming it I want to skip the books key, so the structure will be more flat [book1, book2] (not [books => [book1, book2]]. I have the following classes:

<?php

class Store
{
    private ?BooksCollection $booksCollection = null;

    public function __construct(?BooksCollection $booksCollection = null)
    {
        $this->booksCollection = $booksCollection;
    }

    public function getBooksCollection(): ?BooksCollection
    {
        return $this->booksCollection;
    }
}

class BooksCollection
{
    /** @var Book[] */
    private array $books;

    public function __construct(Book ...$books)
    {
        $this->books = $books;
    }

    public function getBooks(): array
    {
        return $this->books;
    }
}

class Book
{
    private string $title;

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

    public function getTitle(): string
    {
        return $this->title;
    }
}

and serialization config:

Store:
  exclusion_policy: ALL
  properties:
    booksCollection:
      type: BooksCollection
BooksCollection:
  exclusion_policy: ALL
  properties:
    books:
      type: array<int, Book>
Book:
  exclusion_policy: ALL
  properties:
    title:
      type: string

The test I want to pass:

<?php

use JMSSerializerArrayTransformerInterface;
use SymfonyBundleFrameworkBundleTestKernelTestCase;

class StoreSerializeTest extends KernelTestCase
{
    /** @var ArrayTransformerInterface */
    private $serializer;

    protected function setUp(): void
    {
        self::bootKernel();
        $this->serializer = self::$kernel->getContainer()->get('jms_serializer');
    }

    public function testSerialization(): void
    {
        $store = new Store(new BooksCollection(new Book('Birdy'), new Book('Lotr')));

        $serializedStore = $this->serializer->toArray($store);
        $storeUnserialized = $this->serializer->fromArray($serializedStore, Store::class);

        self::assertSame(
            [
                'books_collection' => [
                    ['title' => 'Birdy'],
                    ['title' => 'Lotr']
                ]
            ],
            $serializedStore
        );
        self::assertEquals($store, $storeUnserialized);
    }
}

As you can see below the test is failing. How can I get rid of one nesting ‘books’? jms serializer

The main idea I had, was to use EventSubscriberInterface and onPreSerialize event, but I really can’t figure out how can I replace an object BooksCollection with an array made of its own property books. Is there anyone who already know how to do it?

Answer

Finally, I figured it out. I implemented SubscribingHandlerInterface

<?php

use JMSSerializerContext;
use JMSSerializerGraphNavigatorInterface;
use JMSSerializerHandlerSubscribingHandlerInterface;
use JMSSerializerJsonDeserializationVisitor;
use JMSSerializerJsonSerializationVisitor;
use Book;
use BooksCollection;

class BooksCollectionHandler implements SubscribingHandlerInterface
{
    public static function getSubscribingMethods(): array
    {
        return [
            [
                'type' => BooksCollection::class,
                'format' => 'json',
                'method' => 'serialize',
                'direction' => GraphNavigatorInterface::DIRECTION_SERIALIZATION,
            ],
            [
                'type' => BooksCollection::class,
                'format' => 'json',
                'method' => 'deserialize',
                'direction' => GraphNavigatorInterface::DIRECTION_DESERIALIZATION,
            ]
        ];
    }

    public function serialize(
        JsonSerializationVisitor $visitor,
        BooksCollection $booksCollection,
        array $type,
        Context $context
    ) {
        return $visitor->visitArray($booksCollection->getBooks(), ['name' => 'array'], $context);
    }

    public function deserialize(
        JsonDeserializationVisitor $visitor,
        array $data,
        array $type,
        Context $context
    ): BooksCollection {
        $collection = [];

        foreach ($data as $book) {
            $collection[] =
                $visitor->getNavigator()->accept($book, ['name' => Book::class], $context);
        }

        return new BooksCollection(...$collection);
    }
}

service config:

    books_handler:
        class: BooksCollectionHandler
        tags:
            - { name: jms_serializer.subscribing_handler }

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