title: Checking which form field value has changed Symfony 3
body: <p>I need to check inside the FormType which field has changed. Is there any method to do it? I've searched for a while, then tried to get edited entities field in few ways (with form events too) to catch the edited fields, but no simple result.</p>
  
  <p>Is there any way to do it easy, or I need to be more creative in making such thing? The best it would be, if I can get an example with entity type, but any clue would be great.</p>
  
  <p>P.S. I cant do it on client-side - I must do it on server side for particular reason.</p>