Doctrine & TreeView

Hi treeview does not work with doctrine

My Entity

class MaterialCategory implements IEntity
{
    use SmartObject;
    use TId;
    use TName;
    use TSlug;

    /**
     * @var MaterialCategory|null
     * @ORM\ManyToOne(targetEntity="MaterialCategory", inversedBy="children")
     * @ORM\JoinColumn(name="parent_id", referencedColumnName="id", onDelete="SET NULL")
     */
    private $parent;

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

    /**
     * @ORM\OneToMany(targetEntity="Material", mappedBy="category",cascade={"all"})
     */
    private $material;

    /**
     * MaterialCategory constructor.
     */
    public function __construct()
    {
        $this->children = new ArrayCollection();
        $this->material = new ArrayCollection();
    }

    /**
     * @return MaterialCategory|null
     */
    public function getParent(): ?MaterialCategory
    {
        return $this->parent;
    }

    /**
     * @param MaterialCategory|null $parent
     * @return $this
     */
    public function setParent(?MaterialCategory $parent)
    {
        $this->parent = $parent;
        return $this;
    }

    /**
     * @return Collection
     */
    public function getChildren(): Collection
    {
        return $this->children;
    }
}

DQL

SELECT MaterialMaterialCategory FROM app\modules\Materials\entities\MaterialCategory MaterialMaterialCategory WHERE MaterialMaterialCategory.parent IS NULL

Datagrid show only root rows.
hasChildrenCallback and getChildrenCallback never run (callbacks use $entity->getChildren()

Start by reproducing the shown DQL query with the MaterialCategory entity and tracing the TreeView hasChildrenCallback and getChildrenCallback behavior. Compare the Doctrine entity mappings with the datagrid's tree-loading path; done means root rows display their children through the callbacks without breaking the Doctrine-backed grid.