how to insert into junction table when many to many with doctrine? - symfony

Question

I am trying to insert into a junction table called post_post_category which is based on Post and PostCategory tables [many to many], i manage to execute the insert but the problem is that when i add a new post it creates a new category.
Post Entity:
class Post
{
...
/**
* #ORM\ManyToMany(targetEntity="PostCategory", cascade={"persist"})
* #ORM\JoinTable(name="post_post_category",
* joinColumns={#ORM\JoinColumn(name="post_id", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="post_category_id", referencedColumnName="id")}
* )
*/
private $categories;
public function __construct() {
$this->categories = new ArrayCollection();
}
...
public function getCategories(): ?PostCategory
{
return $this->categories;
}
public function addCategory(PostCategory $category): self
{
$this->categories->add($category);
return $this;
}
}
Category Entity:
class PostCategory
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\Column(type="string", length=60)
*/
private $category_description;
public function getId()
{
return $this->id;
}
public function getCategoryDescription(): ?string
{
return $this->category_description;
}
public function setCategoryDescription(string $category_description): self
{
$this->category_description = $category_description;
return $this;
}
}
Controller:
...
$category->setCategoryDescription('New category');
$post->addCategory($category);
$database_manager->persist($post);
$database_manager->flush();
How do i insert an existing category in junction table?

Answer 1

to add an existing category to a Post you will have to retrieve the category from the database
$category = $em->getRepository('AppBundle:PostCategory')->find($categoryId);
$post->addCategory($category);