Maintaining OneToMany links with a form - symfony

Question

Imagine these 2 entities
Intervention
- items # OneToMany (no cascade)
addItem()
removeItem()
Item
- intervention # ManyToOne
When I'm doing an Intervention I want to select the Items concerned.
I use an Intervention form in which I can attach/unattach items
->add('items', EntityIdType::class, array(
'class' => Item::class,
'multiple' => true,
))
When the form is submitted, I see Doctrine calls my Intervention's addItem(), removeItem()
But when I empty any previously attached items (thus sending null as items), Doctrine tells me:
Neither the property "items" nor one of the methods "addItem()"/"removeItem()", "setItems()", "items()", "__set()" or "__call()" exist and have public access in class "AppBundle\Entity\Intervention".
The first question is: Why Doctrine is not finding my accessors when I send a null item list ?

Answer 1

My workaround for now is to implement a setItems() doing the adds/removes:
/**
* Set items
*
* #param $items
*
* #return Intervention
*/
public function setItems($items)
{
foreach ($this->items as $item) {
$this->removeItem($item);
}
if ($items) {
foreach ($items as $item) {
$this->addItem($item);
}
}
return $this;
}

Answer 2

I think you need to use ArrayCollection in your other side of the ManyToOne relationship.
Your AppBundle\Entity\Item entity class needs to have:
use AppBundle\Entity\Intervention;
//...
/**
* #ORM\ManyToOne(targetEntity="AppBundle\Entity\Intervention", inverseBy="items")
*/
private $intervention;
/**
* #param Intervention $intervention
*/
public function setIntervention(Intervention $intervention){
$this->intervention = $intervention;
}
/**
* #return Intervention
*/
public function getIntervention(){
return $this->intervention;
}
Then in the AppBundle\Entity\Intervention entity class:
use Doctrine\Common\Collections\ArrayCollection;
//...
/**
* #ORM\OneToMany(targetEntity="AppBundle\Entity\Item", mappedBy="intervention")
*/
private $items;
public function __construct(){
$this->items = new ArrayCollection();
}
public function getItems(){
return $this->items;
}
public function setItems($items){
$this->items = $items;
}