PHP dynamic multidimensional array or objects - php

Question

I'm trying to create a recursive function (or method) that stores a sub-tiered navigation in an array variable or object. Here is what I have:
class Navigation extends Database
{
function build($parent_id = 0)
{
$query = 'SELECT id, name, href, parent_id
FROM navigation
WHERE parent_id = '.$parent_id.'
ORDER BY name';
$results = $db->query($query);
while ($row = $results->fetch_object()) {
$nav[$row->id] = $row;
// echo $row;
$this->build($row->id);
}
return $nav;
}
}
If you comment out the echo $row everything works fine. So what I want it to do in a three tier navigation is this:
Array
(
[1] => stdClass Object
(
[id] => 1
[name] => Home
[href] => home.php
[parent_id] => 0
)
[2] => stdClass Object
(
[id] => 2
[name] => Company
[href] => company.php
[parent_id] => 0
)
[4] => stdClass Object
(
[id] => 4
[name] => Company Vision
[href] => company_vision.php
[parent_id] => 2
)
[5] => stdClass Object
(
[id] => 5
[name] => Company Goals
[href] => company_goals.php
[parent_id] => 2
)
[3] => stdClass Object
(
[id] => 3
[name] => Products
[href] => products.php
[parent_id] => 0
)
[6] => stdClass Object
(
[id] => 6
[name] => Products Shoes
[href] => products_shoes.php
[parent_id] => 3
)
[7] => stdClass Object
(
[id] => 7
[name] => Nike
[href] => products_shoes_nike.php
[parent_id] => 6
)
)
Just as an example, so the array would dynamically do this:
$nav[$row->id] = $row; // Home
$nav[$row->id] = $row; // Company
$nav[2][$row->id] = $row; // Company Vision
$nav[2][$row->id] = $row; // Company Goals
$nav[$row->id] = $row; // Products
$nav[3][$row->id] = $row; // Products Shoes
$nav[3][6][$row->id] = $row; // Products Shoes Nike
Thanks in advance.
Question: How do you make a recursive function/method and store the recursive information in a variable rather than echoing the results?
Issues:
(a) PHP overwrites the variable every time it calls itself recursively
(b) A solution would be dynamically creating an array on the fly, but I don't know if that is possible

Answer 1

I suspect you need the nested sets algorithm http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/