title: How to change entity class in form type?
body: <p>I have tree almost identical entity classes: A, B, C (they all extends one superclass via Doctrine class table inheritance).</p>
  
  <p>And i have a form that allows to choose proper entity class via ChoiceType. In fact i need possibility to change entity class via form on entity creation (when its not persisted)</p>
  
  <p>I cant figure out how to create controller action that will hande:</p>
  
  <ul>
  <li>creation of new A/B/C entity</li>
  <li>changing the entity class (when i change class field - form will submit)</li>
  <li>persisting the entity</li>
  </ul>
  
  <p><strong>Update</strong>
  I updated description and found solution (see lower)</p>