Self JOIN query with Symfony entity - symfony

Question

Here's my table :
My Category entity (without getter/setter):
/**
* #var int
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="name", type="string", length=255)
*/
private $name;
/**
* #var string
*
* #ORM\Column(name="slug", type="string", length=255, nullable=true)
*/
private $slug;
/**
* #var int
* #Gedmo\TreeLeft
* #ORM\Column(name="lft", type="integer")
*/
private $lft;
/**
* #var int
* #Gedmo\TreeLevel
* #ORM\Column(name="lvl", type="integer")
*/
private $lvl;
/**
* #var int
* #Gedmo\TreeRight
* #ORM\Column(name="rgt", type="integer")
*/
private $rgt;
/**
* #Gedmo\TreeRoot
* #ORM\ManyToOne(targetEntity="Category")
* #ORM\JoinColumn(name="root", referencedColumnName="id", onDelete="CASCADE")
*/
private $root;
/**
* #Gedmo\TreeParent
* #ORM\ManyToOne(targetEntity="Category", inversedBy="children")
* #ORM\JoinColumn(name="parent", referencedColumnName="id", onDelete="CASCADE")
*/
private $parent;
/**
* #ORM\OneToMany(targetEntity="Category", mappedBy="parent")
* #ORM\OrderBy({"lft" = "ASC"})
*/
private $children;
In my controller, if I do this :
$category= $this->container->get('app.category.manager')->getCategoryBySlug($category_slug);
$root = $term->getRoot();
Doctrine execute 2 queries, one for the category itself, and one for the root of the category. I would like to create my own repository function to join the 2 entities in one query. I've tried so many things with the query builder, now I'm completly lost.

Answer 1

First, create a custom Repository class for your entity.
Then, paste the a method like the following into:
class CategoryRepository extends EntityRepository
{
public function getRootByCategorySlug($slug)
{
return $this->getEntityManager()
->createQueryBuilder()
->from('YourBundle:Category', 'c')
->where('c.slug = :slug')
->setParameter('slug', $slug)
->leftJoin('c.root', 'r') // Join the association
->select('r') // Fetch the association only
->getQuery()
->getResult()
;
}
}
And use it like follows:
$repo = $this->getDoctrine()->getManager()->getRepository('YourBundle:Category');
$rootCategory = $repo->getRootByCategorySlug('your_slug');