Laravel multilevel menu doesn't work - php

Question

I have created multilevel menu by this example (first reply):
How to create a database-driven multi-level navigation menu using Laravel
I'm always getting empty array. Here's my database structure (database's name is also "structure")
structure_id and parent_id are relevant.
Here's my code:
App/navigation.php
<?php
namespace App;
use DB;
use Illuminate\Database\Eloquent\Model;
class Navigation extends Model {
/**
* The database table used by the model.
*
* #var string
*/
protected $table = 'structure';
public function parent() {
return $this->hasOne('structure', 'structure_id', 'parent_id');
}
public function children() {
return $this->hasMany('structure', 'parent_id', 'structure_id');
}
public static function tree() {
return static::with(implode('.', array_fill(0, 4, 'children')))->where('parent_id', '=', NULL)->get();
}
}
and the Controller:
app/http/controllers/structurecontroller.php
<?php
namespace App\Http\Controllers\Superuser;
use App\Http\Controllers\Controller;
use App\Navigation;
use App\Structure as Model;
class StructureController extends Controller
{
/**
* Allow only for logged in
* DashboardController constructor.
*/
public function __construct()
{
$this->middleware('auth');
}
public function index()
{
//$model = new Model();
//$items = $model->getStructure();
$items = Navigation::tree();
var_dump($items);exit;
return view('superuser.structure', ['items' => $items]);
}
}
I'm pretty sure, I have some data in database. So, what's the problem there? I'm getting always empty array from database. Thank for help

Answer 1

It's probably your database structure--you're declaring parent_id as NOT NULL, with a default of 0. In your tree function you then do this:
...->where('parent_id', '=', NULL)->get();
I'm going to guess that the "0" is not resolving to NULL like you intended.

Answer 2

// Do not forget to add import: App\structure
public function parent() {
return $this->hasOne('App\structure', 'structure_id', 'parent_id');
}