gistfile1.php

<?php


// ...
class MyAwesomeController extends Controller
{
    public function uselessAction(Request $request)
    {
        $user = new User();
        
        $form = $this->createFormBuilder($user)
            // ...
            ->getForm();
        
        $form->bindRequest($request);
        if ($form->isValid()) {
            $em = $this->getDoctrine()->getManager();
            
            $em->persist($user);
            
            $em->flush();
            
            $user->getId(); // gives the id
            return;
        }
    }
}