Symfony: Entities and Class Implements - php

Question

Suppose I want to have two entities in my database, a Box and an Object. I can have different boxes and within each box I can add multiple Objects.
(For simplicity, I've missed out the getters, setters, $id, etc in the code examples)
Box entity
namespace AppBundle\Entity;
class Box {
...
/**
* #ORM\OneToMany(targetEntity="Object", mappedby="box")
*/
private $objects;
}
Object entity
namespace AppBundle\Entity;
class Object {
...
/**
* #ORM\ManyToOne(targetEntity="Box", mappedby="objects")
*/
private $box;
// The following are assumptions
private $objectType;
private $objectData;
private $theObject;
}
My objects can be multiple types (I want to be able to add new types of objects without touching the database):
A Pen (not an Entity)
class Pen implements ObjectType {
public $color; // In reality this would have set/get
public function whatAmI() {
return "I am a ".$this->color." pen";
}
}
A Remote (not an Entity)
class Remote implements ObjectType {
public $numberOfButtons;
public function whatAmI() {
return "I am a remote with ".$this->numberOfButtons." buttons";
}
public function pressButton() {
...
}
}
ObjectType
interface ObjectType {
public function whatAmI();
}
My question is what is the best way to tie the two bits together? I would like to be able to do the following:
Go through all the objects in my box and call functions which they implement:
$myBox = $em->find('Box', $id);
foreach ($myBox->getObjects() as $object) {
echo $object->whatAmI();
}
Create a new object and add it to my box:
$myPen = new Pen();
$myPen->color = "red";
$myBox->addObject($myPen);
Call functions if I fetch the object directly from the DB:
$myRemote = find('Object', $id); // $id will be of a Remote class
$myRemote->pressButton();