gistfile1.php

class Folder
{
    /**
     * @var Folder
     *
     * @ORM\ManyToOne(targetEntity="Folder", inversedBy="childrenFolders")
     * @ORM\JoinColumn(onDelete="cascade")
     */
    protected $parentFolder;

    /**
     * @var ArrayCollection
     *
     * @ORM\OneToMany(targetEntity="Folder", mappedBy="parentFolder")
     */
    protected $childrenFolders;

   /**
     * @param Folder $parentFolder
     * @return Folder
     */
    public function setParentFolder(Folder $parentFolder)
    {
        $this->parentFolder = $parentFolder;
        return $this;
    }

    /**
     * @return Folder
     */
    public function getParentFolder()
    {
        return $this->parentFolder;
    }

    /**
     * @param Folder $childFolder
     * @return Folder
     */
    public function addChildFolder(Folder $childFolder)
    {
        $this->childrenFolders[] = $childFolder;
        $childFolder->setParentFolder($this);

        return $this;
    }

    /**
     * @return ArrayCollection
     */
    public function getChildrenFolders()
    {
        return $this->childrenFolders;
    }