Doctrine result giving infinite loop - php

Question

Here are my two classes
class Product extends BaseModel{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue
*/
protected $id;
/**
* #ORM\Column(type="string")
*/
protected $name;
/**
* #ORM\Column(type="string")
* #var string
*/
protected $description;
protected $created;
/**
* #ORM\Column(type="string")
* #var string
*/
protected $status;
/**
* #ORM\Column(type="decimal", precision=5, scale=4)
* #var float
*/
protected $price;
/**
* #ORM\ManyToOne(targetEntity="Category")
* #ORM\JoinColumn(name="category_id", referencedColumnName="id")
*/
private $category;
}
and
class Category extends BaseModel {
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue
*/
protected $id;
/**
* #ORM\Column(type="string")
*/
protected $category;}
as I perform this
$fullyQualifiedClassName = '\\System\\App\\Model\\Product';
$object = new $fullyQualifiedClassName();
$objectRepository = $this->entityManager->getRepository($fullyQualifiedClassName);
$results = $objectRepository->findAll();
print_r($results);
the application enters an infinite loop giving for each product its category associated and for each category its products and so on until the app breaks.
how can I fix this ?
thanks in advance.