Aggregate values on API Platform response - symfony

Question

Similar to this question, I am using API Platform with Doctrine entities - I have an Entity which contains a value:
/**
* #ApiResource()
*/
class Credit
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\Column(type="integer")
*/
private $value;
}
I would like to retrieve the sum of this value and return it in the top level element of the response when querying for a collection:
{
"#context": "/api/contexts/Credit",
"#id": "/api/credits",
"#type": "hydra:Collection",
"hydra:member": [
{
"#id": "/api/credits/1",
"#type": "Credit",
"id": 1,
"value": 200,
"createdAt": "2019-03"
},
{
"#id": "/api/credits/2",
"#type": "Credit",
"id": 2,
"value": 200,
"createdAt": "2019-04"
}
],
"hydra:totalItems": 2,
"totalValues": 400
}
However, I would like to achieve this using a copy of the query instead of summing the values after the execution to maintain the same totalValues amount when pagination is applied - much the same way that hydra:totalItems will always return the total number of items.
What would be the best way to achieve this?

Answer 1

You can create a CreditCollectionNormalizer:
<?php
namespace App\Serializer\Normalizer;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerAwareInterface;
class CreditCollectionNormalizer implements NormalizerInterface, NormalizerAwareInterface
{
public const RESOURCE_CLASS = \App\Entity\Credit::class;
private const ALREADY_CALLED = 'CREDIT_COLLECTION_NORMALIZER_ALREADY_CALLED';
private NormalizerInterface $normalizer;
public function __construct(NormalizerInterface $normalizer)
{
$this->normalizer = $normalizer;
}
public function normalize($object, string $format = null, array $context = []): array
{
$context[self::ALREADY_CALLED] = true;
$data = $this->normalizer->normalize($object, $format, $context);
if ('collection' === $context['operation_type'] &&
'get' === $context['collection_operation_name'] &&
self::RESOURCE_CLASS == $context['resource_class']) {
$balance = 0;
foreach ($object as $item) {
$balance += $item->amount;
}
$data['hydra:meta']['balance'] = $balance;
}
return $data;
}
public function supportsNormalization($data, string $format = null, array $context = []): bool
{
return $this->normalizer->supportsNormalization($data, $format, $context);
}
public function setNormalizer(NormalizerInterface $normalizer)
{
if ($this->normalizer instanceof NormalizerAwareInterface) {
$this->normalizer->setNormalizer($normalizer);
}
}
}
Then register it as a CollectionNormalizer decorator in services.yaml:
services:
App\Serializer\Normalizer\CreditCollectionNormalizer:
decorates: 'api_platform.hydra.normalizer.collection'
arguments: [ '#App\Serializer\Normalizer\CreditCollectionNormalizer.inner' ]
public: false
api/credits should now return the following:
{
"#context": "/api/contexts/Credit",
"#id": "/api/credits",
"#type": "hydra:Collection",
"hydra:member": [
{
"#id": "/api/credits/1",
"#type": "Credit",
"id": 1,
"value": 200,
"createdAt": "2019-03"
},
{
"#id": "/api/credits/2",
"#type": "Credit",
"id": 2,
"value": 200,
"createdAt": "2019-04"
}
],
"hydra:totalItems": 2,
"hydra:meta": {
"balance": 400
}
}