Laravel API ResourceCollection WhenLoaded - laravel

Question

I try to include a relationship in my resource array if it has been eager loaded, but don't get it working.
Anyone has an idea, how I can check the relationships in the ResourceCollection?
Database schema looks like this:
Here is my Post Model
class Post extends Model
{
function categories() {
return $this->belongsToMany('App\Category');
}
}
Here is my Category Model
class Category extends Model
{
function posts() {
return $this->belongsToMany('App\Post');
}
}
Here is my Post Controller
Class PostController extends Controller
{
public function index()
{
return new PostResourceCollection(Post::with("categories")->get());
}
}
Here is my Post ResourceCollection
class PostResourceCollection extends ResourceCollection
{
public function toArray($request)
{
return [
'data' => $this->collection->transform(function($page){
return [
'type' => 'posts',
'id' => $page->id,
'attributes' => [
'name' => $page->title,
],
];
}),
//'includes' => ($this->whenLoaded('categories')) ? 'true' : 'false',
//'includes' => ($this->relationLoaded('categories')) ? 'true' : 'false',
];
}
}

Answer 1

Maybe too late, below solution is a workaround for this case:
return [
...,
'includes' => $this->whenLoaded('categories', true),
];
Loading custom attribute:
return [
...,
'includes' => $this->whenLoaded('categories', fn() => $this->categories->name),
];

Answer 2

You relationship is wrong, a post belongs to many categories while a category has many posts so change:
class Category extends Model
{
function posts() {
return $this->belongsToMany('App\Post', 'category_post');
}
}
to
class Category extends Model
{
function posts() {
return $this->hasMany('App\Post', 'category_post');
}
}
Now when you load the post you can load the categories also:
$posts = Post::with('categories')->get();

Answer 3

got it.. That was the missing piece. if anyone has a better solution for this it would be much appreciated.
foreach ($this->collection as $item) {
if ($item->relationLoaded('categories')) {
$included = true;
}