title: Doctrine get all field names with associations
body: <p>I already know how to get field names for entity, but how to get class names for all associations also?</p>
  
  <pre><code>$em-&gt;getClassMetadata('Product')-&gt;getFieldNames();
  </code></pre>
  
  <p>This gets class property only, but I expect to get association names inside nested array, for example if I have customer associated to product I would like to get all customer class property names too.</p>