Laravel recursively get all offsprings of a taxonomy - laravel

Question

I have a table called taxonomies which stores all the taxonomies of products for my ecommerce site. This is how the table looks like:
+--------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | UNI | NULL | |
| parent_id | int(10) unsigned | YES | MUL | NULL | |
| num_products | smallint(6) | NO | | 0 | |
+--------------+------------------+------+-----+---------+----------------+
Now given a taxonomy id, how can I recursively get all its offspring ids? My effort so far:
public function getAllTaxonomyOffspringIds($parent_id, $offspring_ids = array()) {
$taxonomy = Taxonomy::find($parent_id);
if (!is_null($taxonomy)) {
$first_generation_ids = $taxonomy->subtaxonomies()->lists('id');
$offspring_ids = array_merge($offspring_ids, $first_generation_ids);
if (count($first_generation_ids) > 0) {
foreach ($first_generation_ids as $child_id) {
self::getAllTaxonomyOffspringIds($child_id, $offspring_ids);
}
// foreach ($first_generation_ids as $child_id) {
// $child_taxonomy = Taxonomy::find($child_id);
// if (!is_null($child_taxonomy)) {
// $second_generation_ids = $child_taxonomy->subtaxonomies()->lists('id');
// $offspring_ids = array_merge($offspring_ids, $second_generation_ids);
// if (count($second_generation_ids)) {
// }
// }
// }
}
}
return $offspring_ids;
}
But it gives me only the ids of first generation children...

Answer 1

This is actually a width first tree traversal algorithm, and here's the code I've managed to figure out how to:
public function getTaxonomyChildren($id) {
$taxonomy = Taxonomy::find($id);
$child_ids = array();
if (!is_null($taxonomy)) {
$child_ids = $taxonomy->subtaxonomies()->lists('id');
}
return $child_ids;
}
public function getAllTaxonomyOffspringIds($parent_id, $offspring_ids = array()) {
$child_ids = self::getTaxonomyChildren($parent_id);
$offspring_ids = array_merge($offspring_ids, $child_ids);
while (count($child_ids) > 0) {
$temp_ids = array();
foreach ($child_ids as $child_id) {
$temp_ids = array_merge($temp_ids, self::getTaxonomyChildren($child_id));
}
$child_ids = $temp_ids;
$offspring_ids = array_merge($offspring_ids, $child_ids);
}
return $offspring_ids;
}