PHP - Recursive function to find parents of any given parent - issue

Question

I hope somebody can help, this is driving me crazy!

I have a simply recursive PHP function for getting all parents to any given parent for a list of categories. You simply pass it the parent category ID for any given category and it will recursively get all the parents further up the tree.

function getParentCategoriesById($parent_category_id,array $parents = []){
if(empty($parent_category_id)) {
 return [];
}
$parents[] = $parent_category_id;
$parent_category = DB::builder()->table('product_categories')->find($parent_category_id);
if(!empty($parent_category->parent)) {
 getParentCategoriesById($parent_category->parent,$parents);
}
return $parents;}

Let's say category id=100 has 2 parents (33->37), if I dump the $parents array just before the return, the results are:

Array
(
 [0] => 33
 [1] => 37
)

Array
(
 [0] => 33
)

The first array returned is the correct result, but I don't understand how the function is re-running and then instead returning only the first parent.

• C3roe: You are not doing anything with the result of your second getParentCategoriesById call. And the array itself is not modified, you’d have to pass it per reference for that to happen.

Answer 1

You should pass reference to $parents in internal call to getParentCategoriesById()

function getParentCategoriesById($parent_category_id, array &$parents = []) { ... }

• grow.home: Thanks, although due to my PHP version I had to pay the reference in the function definition: private function getParentCategoriesById($parent_category_id,array &$parents = [])
• Nigel Ren: Also no need to return this array.