Doctrine ORM does not persist relations - php

Question

I have a problem persisting relations with doctrine.
This is the process I'm doing:
Create Material object & fill with data
Create PossibleMaterialConfiguration Object & fill with data
Assign PossibleMaterialConfiguration Object to Material Object with
$material->addPossibleMaterialConfiguration($possibleMaterialConfiguration);
Result:
PossibleMaterialConfiguration.material_id is empty!
But when I do it the other way round and assign Material Object to PossibleMaterialConfiguration it does work!
I'm driving crazy! What the hell is going on here? Thanks in advance.
My two entities:
Material.php
/**
* Material
*
* #ORM\Table()
* #ORM\Entity
*/
class Material
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="name", type="string", length=255)
*/
private $name;
/**
* #ORM\OneToMany(targetEntity="PossibleMaterialConfiguration", mappedBy="material", cascade={"persist"})
*/
private $possibleMaterialConfigurations;
PossibleMaterialConfiguration.php
/**
* PossibleMaterialConfiguration
*
* #ORM\Table()
* #ORM\Entity
*/
class PossibleMaterialConfiguration
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #ORM\ManyToOne(targetEntity="Material", inversedBy="possibleMaterialConfigurations")
* #ORM\JoinColumn(name="material_id", referencedColumnName="id")
*/
private $material;
/**
* #var float
*
* #ORM\Column(name="thickness", type="decimal")
*/
private $thickness;
/**
* #var float
*
* #ORM\Column(name="lengthMin", type="decimal")
*/
private $lengthMin;
/**
* #var float
*
* #ORM\Column(name="lengthMax", type="decimal")
*/
private $lengthMax;
/**
* #var float
*
* #ORM\Column(name="widthMin", type="decimal")
*/
private $widthMin;
/**
* #var float
*
* #ORM\Column(name="widthMax", type="decimal")
*/
private $widthMax;

Answer 1

Take a look at the article about owing side in doctrine :
http://docs.doctrine-project.org/en/latest/reference/unitofwork-associations.html
Basically, doctrine won't check the side where is the "mappedBy" annotation.
If you want to do :
$material->addPossibleMaterialConfiguration($possibleMaterialConfiguration);
Then your addPossibleMaterialConfiguration function should be :
function addPossibleMaterialConfiguration($assoc) {
$this->possibleMaterialConfigurations[] = $assoc;
$assoc->setMaterial($this);
}