Removing a child and grandchildren with cascade operation in Symfony2, with Doctrine - php

Question

I've encountered a problem regarding removing objects, or - to be precise - removing their associations in Symfony2.
Let's assume that we've got 3 entities - Parent, Child and a Grandchild.
For the sake of clarity I'll stick to this erhm, naming.
When removing Parent, I want the association between Parent-Child, and Child-Grandchild to be removed, that is, without any additional dirty workaround; I'd like the ORM layer to do the job.
So, without further ado, here are entities with annotations:
class Parent
/**
* #var ArrayCollection
*
* #ORM\OneToMany(targetEntity="Children", mappedBy="Parent")
*/
private $children;
class Children
/**
* #var Parent
*
* #ORM\ManyToOne(targetEntity="Parent", inversedBy="Children")
* #ORM\JoinColumn(name="parent_id", referencedColumnName="id", onDelete="SET NULL")
*/
private $parent;
/**
* #var ArrayCollection
*
* #ORM\OneToMany(targetEntity="Grandchildren", mappedBy="Children")
*/
private $Grandchildren;
class GrandChildren
/**
* #var Children
*
* #ORM\ManyToOne(targetEntity="Children", inversedBy="Grandchildren")
* #ORM\JoinColumn(name="children_id", referencedColumnName="id", onDelete="SET NULL")
*/
private $children;
And here is a simple standard deleteAction of a Parent:
public function deleteAction(Request $request, $id)
{
$form = $this->createDeleteForm($id);
$form->handleRequest($request);
if ($form->isValid()) {
$em = $this->getDoctrine()->getManager();
$parent = $em->getRepository('AppBundle:Parent')->find($id);
if (!$entity) {
throw $this->createNotFoundException('Unable to find Parent entity.');
}
$children = $em->getRepository('AppBundle:Children')->findBy(
array(
'parent' => $id,
)
);
$em->remove($parent);
$em->flush();
}
return $this->redirect($this->generateUrl('parent'));
}
With a code as above, after flush, the relationship between Parent-Children disappears (the join column is nulled), but a relation between Children-Grandchildren remains (i.e. the join column children_id isn't reseted to NULL as in Parent-Children situation, the column remains populated with id's).
So, what is the best way to establish this cascading removal? So that when Parent is removed the inherited associations are removed as well. According to the documentation I should do something like: http://symfony.com/doc/current/cookbook/form/form_collections.html#allowing-tags-to-be-removed
that is - just iterate through it, preferably encapsulate the process.
But still it doesn't look very clean to me, anyone has a better, cleaner solution?
Any insight would be helpful, cheers.