谈谈JSONAPI在PHP中的应用

现在服务端程序员的主要工作已经不再是套模版，而是编写基于 JSON 的 API 接口。可惜大家编写接口的风格往往迥异，这就给系统集成带来了很多不必要的沟通成本，如果你有类似的困扰，那么不妨关注一下 JSONAPI，它是一个基于 JSON 构建 API 的规范标准，一个简单的 API 接口大致如下所示：

JSONAPI

简单说明一下：根节点中的 data 用来放置主对象的内容，其中 type 和 id 是必须要有的字段，用来表示主对象的类型和标识，其它简单的属性统统放置到 attributes 里，如果主对象存在一对一、一对多等关联对象，那么放置到 relationships 里，不过只是通过 type 和 id 字段放置一个链接，关联对象的实际内容统统放置在根接点中的 included 里。

有了 JSONAPI，数据解析的过程变得规范起来，节省了不必要的沟通成本。不过如果要手动构建 JSONAPI 数据还是很麻烦的，好在通过使用 Fractal 可以让实现过程相对自动化一些，上面的例子如果用 Fractal 实现大概是这个样子：

<?php

use League\Fractal\Manager;
use League\Fractal\Resource\Collection;

$articles = [
    [
        'id' => 1,
        'title' => 'JSON API paints my bikeshed!',
        'body' => 'The shortest article. Ever.',
        'author' => [
            'id' => 42,
            'name' => 'John',
        ],
    ],
];

$manager = new Manager();

$resource = new Collection($articles, new ArticleTransformer());

$manager->parseIncludes('author');

$manager->createData($resource)->toArray();

?>

如果让我选最喜爱的 PHP 工具包，Fractal 一定榜上有名，它隐藏了实现细节，让使用者完全不必了解 JSONAPI 协议即可上手。不过如果你想在自己的项目里使用的话，与直接使用 Fractal 相比，可以试试 Fractalistic，它对 Fractal 进行了封装，使其更好用：

<?php

Fractal::create()
   ->collection($articles)
   ->transformWith(new ArticleTransformer())
   ->includeAuthor()
   ->toArray();

?>

如果你是裸写 PHP 的话，那么 Fractalistic 基本就是最佳选择了，不过如果你使用了一些全栈框架的话，那么 Fractalistic 可能还不够优雅，因为它无法和框架本身已有的功能更完美的融合，以 Lavaral 为例，它本身内置了一个 API Resources 功能，在此基础上我实现了一个 JsonApiSerializer，可以和框架完美融合，代码如下：

<?php

namespace App\Http\Serializers;

use JsonSerializable;

use Illuminate\Http\Resources\Json\JsonResource;
use Illuminate\Http\Resources\Json\ResourceCollection;
use Illuminate\Pagination\AbstractPaginator;

class JsonApiSerializer implements JsonSerializable
{
    protected $resource;

    protected $data = [];
    protected $included = [];
    protected $links = [];
    protected $meta = [];

    public function __construct(JsonResource $resource)
    {
        $this->resource = $resource;
    }

    public function jsonSerialize()
    {
        if ($this->resource instanceof ResourceCollection) {
            foreach ($this->resource as $resource) {
                $this->data[] = $this->serialize($resource);
            }
        } else {
            $this->data = $this->serialize($this->resource);
        }

        if ($this->resource->resource instanceof AbstractPaginator) {
            $this->setPagination();
        }

        $result = ['data' => $this->data] + array_filter([
            'included' => array_values($this->included),
            'links' => $this->links,
            'meta' => $this->meta,
        ]);

        return $result;
    }

    protected function serialize(JsonResource $resource)
    {
        $result = [
            'type' => $resource->type,
        ];

        $data = $resource->resolve();

        $link = env('APP_URL') . "/{$resource->type}/{$data['id']}";

        foreach ($data as $key => $value) {
            if ($value instanceof JsonResource) {
                if ($value instanceof ResourceCollection) {
                    foreach ($value as $v) {
                        $result['relationships'][$key]['data'][]
                            = $this->compressResource($v);
                    }
                } else {
                    $result['relationships'][$key]['data']
                        = $this->compressResource($value);
                }

                $result['relationships'][$key]['links'] = [
                    'self' => "{$link}/relationships/{$key}",
                    'related' => "{$link}/{$key}",
                ];
            } elseif ($key == 'id') {
                $result['id'] = (string) $value;
            } else {
                $result['attributes'][$key] = $value;
            }
        }

        $result['links'] = [
            'self' => $link,
        ];

        $result = array_merge($result, $resource->with(request()));
        $result += $resource->additional;

        return $result;
    }

    protected function compressResource(JsonResource $resource)
    {
        $included = $this->serialize($resource);

        $key = $resource->type . ':' . $included['id'];

        if (! isset($this->included[$key])) {
            $this->included[$key] = $included;
        }

        return [
            'type' => $resource->type,
            'id'   => $included['id'],
        ];
    }

    protected function setPagination()
    {
        $paginated = $this->resource->resource->toArray();

        $this->links = [
            'first' => $paginated['first_page_url'] ?? null,
            'prev' => $paginated['prev_page_url'] ?? null,
            'next' => $paginated['next_page_url'] ?? null,
            'last' => $paginated['last_page_url'] ?? null,
        ];

        $this->meta = [
            'current_page' => $paginated['current_page'] ?? null,
            'last_page' => $paginated['last_page'] ?? null,
            'per_page' => $paginated['per_page'] ?? null,
            'total' => $paginated['total'] ?? null,
            'from' => $paginated['from'] ?? null,
            'to' => $paginated['to'] ?? null,
        ];
    }
}

?>

对应的 Resource 基本还和以前一样，只是重定义了父类：

<?php

namespace App\Http\Resources;

use App\Http\Resource;

class ArticleResource extends Resource
{
    public $type = 'articles';

    public function toArray($request)
    {
        return [
            'id' => $this->id,
            'name' => $this->name,
            'author' => new AuthorResource($this->whenLoaded('author')),
        ];
    }
}

?>

对应的父类如下，重定义它的原因在于避免显式调用 JsonApiSerializer：

<?php

namespace App\Http;

use Illuminate\Http\Resources\Json\AnonymousResourceCollection;
use Illuminate\Http\Resources\Json\JsonResource;

use App\Http\Serializers\JsonApiSerializer;

abstract class Resource extends JsonResource
{
    public $type;

    public static function collection($resource)
    {
        return new ResourceCollection($resource, static::class);
    }

    public function toResponse($request)
    {
        return new JsonApiSerializer($this);
    }

    public function __toString()
    {
        return json_encode(new JsonApiSerializer($this));
    }
}

class ResourceCollection extends AnonymousResourceCollection
{
    public function toResponse($request)
    {
        return new JsonApiSerializer($this);
    }

    public function __toString()
    {
        return json_encode(new JsonApiSerializer($this));
    }
}

?>

对应的 Controller 也和原来差不多：

<?php

namespace App\Http\Controllers;

use App\Article;
use App\Http\Resources\ArticleResource;
use App\Http\Serializers\JsonApiSerializer;

class ArticleController extends Controller
{
    protected $article;

    public function __construct(Article $article)
    {
        $this->article = $article;
    }

    public function show($id)
    {
        $article = $this->article->with('author')->findOrFail($id);

        $resource = new ArticleResource($article);

        return $resource;
    }
}

?>

整个过程没有对 Laravel 的架构进行太大的侵入，可以说是目前 Laravel 实现 JSONAPI 的最优解决方案了，有兴趣的可以研究一下 JsonApiSerializer 的实现，虽然只有一百多行代码，但是我却费了好大的力气才实现，可以说是行行皆辛苦啊。