title: Sonata Admin how to read not mapped field?
body: <p>I added fields with the option <code>"mapped" =&gt; false</code> to a SonataAdmin form. </p>
  
  <p>Now I need to access the values of the form fields marked with <code>"mapped" =&gt; false</code> in the method <code>postUpdate</code>. How can I retrieve them?</p>