I'm having a bit of trouble making this work properly when querying with Eloquent, here's the model in question and my problem below:

class Category extends Model {

	public function parent()
	{
		return $this->belongsTo('Category', 'parent_id', 'id');
	}

	public function subCategories()
	{
		return $this->hasMany('Category', 'parent_id', 'id');
	}

} 

Basically, each Category can have subCategories and/or be a parent Category to other Categories.

I'm pretty sure the additional params for belongsTo and hasMany are properly set, although I have tested with other combinations with no success. The 'categories' table has an 'id' and a 'parent_id' fields.

I'm having problems when querying for Categories like so:

$categories = Category::where('parent_id', '=', null)->get(); // this works!

$categories = Category::has('parent')->get(); // this gives me an empty collection - why?

Also, I've been trying to query for Categories with a specific parent Category (via slug):

$subCategories = Category::whereHas('parent', function($query) use ($categorySlug)
{
	$query->where('slug', '=', $categorySlug);
})->get();

but also getting an empty collection, even though it should not be so (I've checked DB data several times).

Am I doing something wrong?