Has many and has many through

Categories

id | title | parent_id

Products

id | title | category_id

The categories table self joins to make sub categories:

id | title | parent_id
 1   art     0
 2   sport   0
 3   brushes 1
 4   paints  1
 5   balls   2

Products then belong to a category, so a football product will belong to the balls category which is a sub category of sport.

I have a product and category model.

On the category model I have a hasManyThrough:

public function products()
{
   return $this->hasManyThrough('Product', 'Category', 'parent_id', 'category_id');
}

I call this via:

Category::with('products')->find($catId);

This all works, I can get all products within a category, the issue arrises when I need to get all products in a sub category, so with the data:

id | title | category_id
1    blue paint 4
2   red paint 4
3   fine brush 3

And calling:

Category::with('products')->find(1); //get all art products

I get blue paint, red paint and fine brush.

The problem occurs when I call a sub category:

Category::with('products')->find(4); //get all paints

I get nothing, I should get blue and red paint.

How can I call I solve this so that I can get all products for a parent or sub category?

via Chebli Mohamed