title: DoctrineODM Priming of Multi-Level References
body: <p>Sorry for the awkward title but I have no better naming for the issue (comments on how to properly name the question are welcome).</p>
  
  <p>Let's say I have 3 Documents:</p>
  
  <ul>
  <li>Category</li>
  <li>Product</li>
  <li>Version</li>
  </ul>
  
  <p>A Category has many Products. A Product has many Versions.
  Now I want to Query for all Categories and list all Products and Versions of each Category.</p>
  
  <p>I know about priming <a href="http://docs.doctrine-project.org/projects/doctrine-mongodb-odm/en/latest/reference/priming-references.html" rel="nofollow">priming</a>.</p>
  
  <p>Is it possible to write a query like:</p>
  
  <pre><code>$qb = $dm-&gt;createQueryBuilder('Category')
      -&gt;field('products')-&gt;prime(true)
      -&gt;field('products.versions')-&gt;prime(true)
  $query = $qb-&gt;getQuery();
  </code></pre>