Try this

$cat = Category::where('parent_id', '=', null)->get()
$cat_kids = $cat->subCategories();
$cat_parent = $cat->parent();

Fetching subCategories and the parent category from already built model objects works fine, the problem is querying as I've described above.

has and whereHas are used to check if there exist at least one related model looking from the One-side to the Many-side.
Check out the generated query. You will understand the error.
At the moment I can not think of an easy solution

Category::whereNotNull('parent_id')->get();

That should do it. As for the other part of the question...writing this off the top of my head so it might need adjusting:

Category::select(DB::raw('pr_category.*, (select c2.slug from pr_category AS c2 where c2.id =  pr_category.parent_id) as parentSlug'))->whereNotNull('parent_id')->where('parentSlug', $parentSlug)->get();

'pr_' being whatever your prefix is. Disclaimer: this might not work xD

Hi,

Was this ever solved. Attempting now and just want to be sure.

Thanks