title: Virtual fields with Cakephp 3
body: <p>I need to have a virtual property in my user entity. I followed the <a href="http://book.cakephp.org/3.0/en/orm/entities.html#creating-virtual-properties">CakePHP book</a>.</p>
  
  <p><strong>UserEntity.php</strong>
      
  
  <pre><code>namespace App\Model\Entity;
  
  use Cake\ORM\Entity;
  
  class User extends Entity {
  
      protected $_virtual = ['full_name'];
  
      protected function _getFullName() {
          return $this-&gt;_properties['firstname'] . ' ' . $this-&gt;_properties['lastname'];
      }
  }
  </code></pre>
  
  <p><strong>In a controller</strong></p>
  
  <pre><code>$users = TableRegistry::get('Users');
  $user = $users-&gt;get(29);
  $firstname = $user-&gt;firstname; // $firstname: "John"
  $lastname = $user-&gt;lastname; // $lastname: "Doe"
  $value = $user-&gt;full_name; // $value: null
  </code></pre>
  
  <p>I followed exactly the book and I only get a <code>null</code> value.</p>