API平台响应上的聚合值

Question

与this question类似，我使用的是带有Doctrine实体的API平台--我有一个包含值的实体：

/**
 * @ApiResource()
 */
class Credit
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="integer")
     */
    private $value; 
}

我想检索这个值的和，并在查询集合时在响应的顶层元素中返回它：

{
    "@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 
}

但是，我希望使用查询的副本来实现这一点，而不是在执行之后对值进行求和，以便在应用分页时保持相同的totalValues数量--这与hydra:totalItems总是返回总项数的方式非常相似。

实现这一目标的最佳途径是什么？

Answer 1

您可以创建一个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);
        }
    }
}

然后将其注册为CollectionNormalizer装饰器在services.yaml中

services:
    App\Serializer\Normalizer\CreditCollectionNormalizer:
        decorates: 'api_platform.hydra.normalizer.collection'
        arguments: [ '@App\Serializer\Normalizer\CreditCollectionNormalizer.inner' ]
        public: false

api/credits现在应该返回以下内容：

{
    "@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
    }
}