How to construct an array recursively based on each parent id - php

Question

I have a nested list of categories which DB looks something like this:
id parent_id title
83 81 test3
86 83 test1
87 83 test2
94 87 subtest2.1
95 87 subtest2.2
...etc...
I need to add all child element ids into the $checked_elements array of each parent id.
So if some specific id is selected, it's automatically added into the array of $checked_elements. Here how it looks like:
I'am stuck with the recursive function, on how to add recursively child items of each parent item id ? My function won't go deeper then the 2nd level, can anyone tell me how to work it out so it will check for all child items ?
private function delete( ){
// Collect all checked elements into the array
$checked_elements = $this->input->post('checked');
// Recursive function to check for child elementts
foreach( $checked_elements as $key => $value ){
// Get records where parent_id is equal to $value (checked item's id)
$childs = $this->categories_model->get_by(array('parent_id' => $value));
// Add found record's id into the array
foreach( $childs as $child ){
$checked_elements[] => $child->id;
}
}
}

Answer 1

You can try passing the accumulator array around by reference:
function collect($ids, &$items) {
foreach($ids as $id){
$items[] = $id;
$childs = $this->categories_model->get_by(array('parent_id' => $id));
collect(array_column($childs, 'id'), $items);
}
return $items;
}
function delete( ){
$items = array();
collect($this->input->post('checked'), $items);
//... delete $items
}
In php 5.5+ you can also use generators in a way similar to this:
function collect($ids) {
foreach($ids as $id) {
yield $id;
$childs = $this->categories_model->get_by(array('parent_id' => $id));
foreach(collect(array_column($childs, 'id')) as $id)
yield $id;
}
function delete( ){
$ids = collect($this->input->post('checked'));
I assume your tree is rather small, otherwise I'd suggest a more efficient approach, like nested sets.
If your php version doesn't support array_column, you can use this shim.