title: JSON API format in API-Platform
body: <p>First of all I want to implement <a href="http://jsonapi.org/" rel="nofollow noreferrer">JSON API</a>. 
  I follow <a href="https://api-platform.com/docs/distribution#bringing-your-own-model" rel="nofollow noreferrer">tutorial on api platform</a> and just like in example create entities and response is like   </p>
  
  <pre><code>{
      "links": {
          "self": "/api/books"
      },
      "meta": {
          "totalItems": 1,
          "itemsPerPage": 30,
          "currentPage": 1
      },
      "data": [
          {
              "id": "/api/books/1",
              "type": "Book",
              "attributes": {
                  "isbn": "9781782164104",
                  "title": "Persistence in PHP with the Doctrine ORM",
                  "description": "This book is designed for PHP developers and architects who want to modernize their skills through better understanding of Persistence and ORM.",
                  "author": "Kévin Dunglas",
                  "publicationDate": "2013-12-01T00:00:00+01:00",
                  "_id": 1
              },
              "relationships": {
                  "reviews": {
                      "data": [
                          {
                              "type": "Review",
                              "id": "/api/reviews/1"
                          }
                      ]
                  }
              }
          }
      ]
  }
  </code></pre>
  
  <p>My <code>api_platform.yaml</code> config </p>
  
  <pre><code>api_platform:
      mapping:
          paths: ['%kernel.project_dir%/src/Entity']
      formats:
          jsonapi:
              mime_types: ['application/vnd.api+json']
  </code></pre>
  
  <p>So i have problem with <code>id</code> filed in <code>data</code>. I get <code>id</code> fields in format <code>api/entityName/id</code> but I just want to get  number(string), just like <a href="http://jsonapi.org/" rel="nofollow noreferrer">in JSON API</a>. So is there some configuration that i miss or is any way to achieve that </p>