Doctrine - Symfony2 | Many to Many targeting the same entity - php

Question

I am trying to create a many-to-many foreign key table relation targeting the same entity.
I have successfully created relations with other entities but I'm having trouble when targeting the same entity.
I read a few stack overflow questions and answers and saw what I was doing was possible..
I based my class of this example - the table unit_relations is empty when i add a parent, but works when I add a child to a unit. I'm assuming because the field has the inversedBy annotation.
What do I need to add to allow bi-drectional updating/inserting?
I tried swapping the joinColums like this answer - nothing...
--
/**
* Unit
*
* #ORM\Table()
* #ORM\Entity(repositoryClass="Acme\DemoBundle\Entity\UnitRepository")
*/
class Unit
{
....
/**
* #ORM\ManyToMany(targetEntity="Unit", inversedBy="parents")
* #ORM\JoinTable(name="unit_relations",
* joinColumns={#ORM\JoinColumn(name="unit_id", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="child_unit_id", referencedColumnName="id")}
* )
*/
private $children;
/**
* #ORM\ManyToMany(targetEntity="Unit", mappedBy="children")
*/
private $parents;
}
is adding inversedBy instead of having mappedBy, with the join columns also swapped, the proper way to do it?
Can someone explain this?
/**
* #ORM\ManyToMany(targetEntity="Unit", inversedBy="parents")
* #ORM\JoinTable(name="unit_relations",
* joinColumns={#ORM\JoinColumn(name="unit_id", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="child_unit_id", referencedColumnName="id")}
* )
*/
private $children;
/**
* #ORM\ManyToMany(targetEntity="Unit", inversedBy="children")
* #ORM\JoinTable(name="unit_relations",
* joinColumns={#ORM\JoinColumn(name="child_unit_id", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="unit_id", referencedColumnName="id")}
* )
*/
private $parents;
EDIT
as requested here's the code showing how I create the relation. I just realized it may because the entity doesn't have an id yet since I'm adding the relation on its creation...
$unit = new \Acme\DemoBundle\Entity\Unit();
/* #var $parentUnit \Acme\DemoBundle\Entity\Unit */
$parentUnit = $this->getDoctrine()->getRepository('AcmeDemoBundle:Unit')->findById($request->get('unitId'));
$unit->addParent($parentUnit);
$entityManager = $this->getDoctrine()->getManager();
$entityManager->persist($unit);
$entityManager->flush();

Answer 1

It doesn't matter, that there is no ID, when you add a parent relations.
I cant in detail explain why this happens, but i think the main problem is, that in Many-To-Many Self-Referencing the attribute with JoinTable annotation is potentially the Master-Entity. You can say, that it "holds" all other relations to this Entity.
You can recieve the bi-directional updating/inserting while changing the function $unit->addParent($parent). Change it as follows:
public function addParent($parent)
{
$this->parents[] = $parent;
$parent->addChild($this); // Add the relation in the proper way
}
That should work fine!
Regards!