DoctrineExtensions/example/app/Entity/Category.php

<?php
namespace Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Gedmo\Mapping\Annotation as Gedmo;
use Doctrine\ORM\Mapping as ORM;

/**
 * @Gedmo\Tree(type="nested")
 * @ORM\Table(name="ext_categories")
 * @ORM\Entity(repositoryClass="Entity\Repository\CategoryRepository")
 * @Gedmo\TranslationEntity(class="Entity\CategoryTranslation")
 */
class Category
{
    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue
     */
    private $id;

    /**
     * @Gedmo\Translatable
     * @ORM\Column(length=64)
     */
    private $title;

    /**
     * @Gedmo\Translatable
     * @ORM\Column(type="text", nullable=true)
     */
    private $description;

    /**
     * @Gedmo\Translatable
     * @Gedmo\Slug(fields={"title"})
     * @ORM\Column(length=64, unique=true)
     */
    private $slug;

    /**
     * @Gedmo\TreeLeft
     * @ORM\Column(type="integer")
     */
    private $lft;

    /**
     * @Gedmo\TreeRight
     * @ORM\Column(type="integer")
     */
    private $rgt;

    /**
     * @Gedmo\TreeParent
     * @ORM\ManyToOne(targetEntity="Category", inversedBy="children")
     * @ORM\JoinColumn(name="parent_id", referencedColumnName="id", onDelete="SET NULL")
     */
    private $parent;

    /**
     * @Gedmo\TreeRoot
     * @ORM\Column(type="integer", nullable=true)
     */
    private $root;

    /**
     * @Gedmo\TreeLevel
     * @ORM\Column(name="lvl", type="integer")
     */
    private $level;

    /**
     * @ORM\OneToMany(targetEntity="Category", mappedBy="parent")
     */
    private $children;

    /**
     * @Gedmo\Timestampable(on="create")
     * @ORM\Column(type="datetime")
     */
    private $created;

    /**
     * @Gedmo\Timestampable(on="update")
     * @ORM\Column(type="datetime")
     */
    private $updated;

    /**
     * @ORM\OneToMany(
     *   targetEntity="CategoryTranslation",
     *   mappedBy="object",
     *   cascade={"persist", "remove"}
     * )
     */
    private $translations;

    public function __construct()
    {
        $this->children = new ArrayCollection();
        $this->translations = new ArrayCollection();
    }

    public function getTranslations()
    {
        return $this->translations;
    }

    public function addTranslation(CategoryTranslation $t)
    {
        if (!$this->translations->contains($t)) {
            $this->translations[] = $t;
            $t->setObject($this);
        }
    }

    public function getSlug()
    {
        return $this->slug;
    }

    public function getId()
    {
        return $this->id;
    }

    public function setTitle($title)
    {
        $this->title = $title;
    }

    public function getTitle()
    {
        return $this->title;
    }

    public function setDescription($description)
    {
        $this->description = $description;
    }

    public function getDescription()
    {
        return $this->description;
    }

	public function setParent($parent)
    {
        $this->parent = $parent;
    }

    public function getParent()
    {
        return $this->parent;
    }

    public function getRoot()
    {
        return $this->root;
    }

    public function getLevel()
    {
        return $this->level;
    }

    public function getChildren()
    {
        return $this->children;
    }

    public function getLeft()
    {
    	return $this->lft;
    }

	public function getRight()
    {
        return $this->rgt;
    }

    public function getCreated()
    {
        return $this->created;
    }

    public function getUpdated()
    {
        return $this->updated;
    }

    public function __toString()
    {
        return $this->getTitle();
    }
}