title: What is the correct JSONAPI way to post multiple related entities in a single request?
body: <p>At some point in my hypothetical app, I want to create multiple related entities of different types in a single request, for efficiency sake. In the example below I serialize the request in a way that it contains the data about the new User as well as its related Avatar.</p>
  
  <pre><code>// POST /api/users
  {
      data: {
          attributes: { ... },
          type: 'user',
          relationships: {
              avatar: {
                  data: {
                      attributes: { ... }
                      type: 'avatar',
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>The question is, what would be the correct/recommended way (if there's any) to do that in JSONAPI?</p>