title: Symfony2 ACL problems
body: <p>I've been trying to implement ACL in a system I'm developing and
  had several problems. This is mostly because the total lack of
  documentation on the subject. It'd be really nice if we could have
  more info on this complex and fundamental component. In any case, I'd
  be happy to write something once I understand</p>
  
  <p>Anyway, the problems I'm having are the following:
  1. I have a role with Class-Field-Scope ACE to view and edit a field
  of an object. When I check in the view using this:
  isGranted('VIEW', object, 'myField')</p>
  
  <p>It's always false. Shouldn't class-scope apply to all instance of the
  class? I'm not really sure how this scope works.</p>
  
  <ol>
  <li>When I delete a group, I want to delete all ACL entries related to
  that group. I've tried like this:
  $aclProvider->deleteAcl(ObjectIdentity::fromDomainObject($group))</li>
  </ol>
  
  <p>It works. Then I try to create a new group. The group gets created,
  but the ACL setup fails with this error:</p>
  
  <p>Notice: Undefined offset: 0 in Project/vendor/symfony/src/Symfony/
  Component/Security/Acl/Dbal/MutableAclProvider.php line 850</p>
  
  <p>Any help is greately appreciated! </p>