Use existing database entry for foreign key in Doctrine - php

Question

Given already persisted objects for categories. How do one reuse the existing categories in a one-to-many relationship in new objects when only the id of the cateories is known
/** #Entity() */
class Category {
/**
* #var string
* #\Doctrine\ORM\Mapping\Column(type="string")
*/
private $name;
/** #var string
* #\Doctrine\ORM\Mapping\Id()
* #\Doctrine\ORM\Mapping\Column(type="string")
*/
private $id;
/**
* Category constructor.
* #param string $name
* #param string $id
*/
public function __construct($name, $id)
{
$this->name = $name;
$this->id = $id;
}
/**
* #return string
*/
public function getName()
{
return $this->name;
}
/**
* #return string
*/
public function getId()
{
return $this->id;
}
}
And now I have lets say two categories id=1 -> fiction and id=2 -> english book.
Now I know the ids of the categories and want to save the one-to-many relations in my Book object.
/** #Entity() */
class Book {
/** #var mixed
* #\Doctrine\ORM\Mapping\OneToMany()
*/
private $categories;
/** #var string */
private $title;
/**
* Book constructor.
* #param mixed $categories
* #param string $title
*/
public function __construct($categories, $title)
{
$this->categories = $categories;
$this->title = $title;
}
/**
* #return mixed
*/
public function getCategories()
{
return $this->categories;
}
/**
* #return string
*/
public function getTitle()
{
return $this->title;
}
}
Is it possible to create and persist a book object by hand with references an existing and already persisted object from which I do only know the id?

Answer 1

You can't achieve this without retrieving at least a Reference proxy :
$categoriesRefs = ['english' => 1, 'fiction' => 2];
$categories = [];
foreach($categoriesRefs as $ref){
$categories[] = $em->getReference('Namespace\Entity\Category', $ref));
}
$book = new Book($categories, 'title');
$em->persist($book);
$em->flush();
You can store categories without fetching the whole Category objects.
Read more about reference proxy.