SQL Query and PHP manipulation with Nested Set Model - php

Question

I was reading this article, http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/.
I wanted to give a simple example and then ask you how do I get the desired result? So here is the example:
+---------+-----------------------------+
| product_id | product_name |
+---------+-----------------------------+
| 1 | Example Product |
+---------+-----------------------------+
+---------+-----------------------------+
| product_id | category_id |
+---------+-----------------------------+
| 1 | 2 |
| 1 | 4 |
+---------+-----------------------------+
+-------------+--------------------+------+------+
| category_id | name | lft | rgt |
+-------------+--------------------+------+------+
| 1 | Electronics | 1 | 8 |
| 2 | Televisions | 2 | 3 |
| 3 | Portable Electronics | 4 | 7 |
| 4 | CD Players | 5 | 6 |
+-------------+--------------------+------+------+
I want to be able to display the following result in HTML after querying and then manipulating the data in PHP:
"Example Product" Categories:
Electronics
Televisions
Portable Electronics
CD Players
Can you help walk me through the query and manipulation in PHP to achieve this result?
Some specifics to think about:
Notice how both categories are under Electronics, but "Electronics" appears only once here, displaying each of the subcategories it belongs to below
The result should eventually be a PHP multi-dimensional array with the category containing an array of sub-categories and each sub-category containing an array of sub-subcategories if they exist.
I imagine printing the depth will be very important for constructing the right tree in HTML.

Answer 1

I thought this was a nice challenge .. here's my solution:
Basically: read a node, then all following nodes with a rgt smaller than your rgt are your children, do this recursively.
I've used a peek/consume to read from mysql like you normally would.
The script will break or loop if the query gives no results, or if the data-set is broken.
class NestedNodeReader {
private $mysql_result;
private $peeked = false;
private $last_peek;
public function __construct($mysql_result) {
$this->mysql_result = $mysql_result;
}
public function getTree() {
$root = $this->consume();
$root["children"] = $this->getSubTree($root["rgt"]);
return $root;
}
private function getSubTree($stop_at) {
$nodes = array();
$node = $this->peek();
while ($node["rgt"] < $stop_at) {
$node = $this->consume();
$node["children"] = $this->getSubTree($node["rgt"]);
$nodes[] = $node;
$node = $this->peek();
if (false === $node) {
break;
}
}
return $nodes;
}
private function peek() {
if (false === $this->peeked) {
$this->peeked = true;
$this->last_peek = mysql_fetch_assoc($this->mysql_result);
}
return $this->last_peek;
}
private function consume() {
if (false === $this->peeked) {
return mysql_fetch_assoc($this->mysql_result);
} else {
$this->peeked = false;
return $this->last_peek;
}
}
}
$query = "SELECT node.name, node.lft, node.rgt
FROM nested_category AS node,
nested_category AS parent
WHERE node.lft BETWEEN parent.lft AND parent.rgt
AND parent.name = 'ELECTRONICS'
ORDER BY node.lft;"
$mysql_result = mysql_query($query);
$nnr = new NestedNodeReader($mysql_result);
print_r($nnr->getTree());