belongsToMany with parent-child relationship in Laravel 5 - php

Question

I have two models that are related to each other with a belongsToMany relationship. The models are Game and Category. Of course, the tables for both are games and categories. The Category model, has its own parent-child relationship.
Basically this is my "simplified" structure:
Table game:
id unsigned integer
name string
Table categories:
id unsigned integer
name string
parent_id unsigned integer nullable
The parent_id column is null when the category has no parent, but it has an existing id referencing a row in the same table if it is a children of some other category.
Table category_game
category_id unsigned integer
game_id unsigned integer
The category_id column, references id on categories table. It should reference only the top category that a game belongs to. A game can belong to many different categories, but in the pivot table, there should only be a reference to the parents categories. For example if I had this structure of categories:
Category 1
Category 2
Category 4
Category 3
Category 9
Category 5
Category 6
Category 7
Category 8
I would like to have the following information for my games 1 and 2:
category_id game_id
3 1
5 1
1 2
And that should mean that my game 1 has categories: 3, 9, 5, 6, 7 and 8.
While my game 2 has categories: 1, 2, 4, 3 and 9
I understand that my Laravel models should have this:
class Game {
public function categories(){
return $this->belongsToMany( Category::class );
}
}
class Category{
public function games(){
return $this->belongsToMany( Game::class );
}
}
But I don't know how to retrieve the children categories using Eloquent. I know the belongsToMany method has more parameters that might help with my problem, but I don't know how to use them.

Answer 1

Model categoryGame for table category_game
class CategoryGame{
public function childCategories() {
return $this->hasMany(Category::class, 'parent_id','category_id');
}
}
You can access
$games = App\CategoryGame::all();
foreach ($games as $game ) {
foreach ($game->childCategories as $category) {
echo $category->name;
}
}
Let me know if not works

Answer 2

Extend your models:
class Category {
public function children() {
return $this->hasMany(Category::class, 'parent_id');
}
}
class Game {
public function getAllCategoriesAttribute() {
$result = collect();
$children = function($categories) use(&$result, &$children) {
if($categories->isEmpty()) return;
$result = $result->merge($categories);
$children($categories->pluck('children')->collapse());
};
$children($this->categories);
return $result;
}
}
Then you can access the categories like this:
Game::find($id)->allCategories;