Nested Comments using Redis. Rely on the Owlient Redis extension

Comments.php

<?php
/**
 * A Nested Comments manager using Redis only
 * @author Michel Bartz <michel.bartz@manwin.com>
 * @date 01/28/2011
 */
class Comments
{
	private $_redis;

	public function __construct() {
		$this->_redis = new Redis();
		$this->_redis->connect("localhost", 6379);	
	}
	/**
	 * Save a new comment
	 * @param int $itemId Item on which the comment is made
	 * @param String $comment The comment itself
	 * @param String $username The username of the comment author
	 * @param int $userId The user id of the comment author
	 * @param int $parentId The ID of the direct parent comment, 0 if none.
	 * @return int The comment ID
	 */
	public function save($itemId, $comment, $username, $userId,  $parentId = 0) {
		//To force the re-fetching of the comment tree on the next getComments() call
		$this->_redis->del("item:" . $itemId. " :parsedComments");

		$isMasterComment = false;
		if(!$parentId) {
			$isMasterComment = true;
			$parentId = $itemId;
		} else {
			$this->_redis->hSet("comment:" . $parentId, "hasChildren", 1);
		}

		$data = array("id" => $this->_getCommentId(),
		   			  "parentId" => $parentId,	
					  "user_id" => $userId,
					  "username" => $username,
					  "content" => $comment,
					  "itemId" => $itemId,
					  "hasChildren" => 0,
					  "time" => time());

		if($isMasterComment) {
			$this->_redis->rPush("item:" . $itemId . ":comments", $data['id']);
		} else { 
			$this->_redis->rPush("thread:" . $parentId, $data['id']);
		}
		$this->_redis->hMSet("comment:" . $data['id'], $data);
		return $data['id'];
	}
	/**
	 * Returns all the comments attached to a given Item ID
	 * @param int $itemId The item id 
	 * @return array The comments
	 */
	public function getComments($itemId) {
		$parsedComments = $this->_redis->get("item:" . $itemId. " :parsedComments");

		if(!$parsedComments) {
			$data = $this->_multiFetch("item:" . $itemId . ":comments");
			$parsedComments = $this->_processComments($data);

			$this->_redis->set("item:" . $itemId. " :parsedComments", serialize($parsedComments));
		} else {
			$parsedComments = unserialize($parsedComments);
		}
		return $parsedComments;
	}
	/**
	 * Recursivly fetch the comment tree
	 * @param array $comments The first comment node
	 * @return array
	 */
	private function _processComments($comments) {
		$curr = array();
		foreach($comments as $comment) {
			if($comment['hasChildren'] === "1") {
				$data = $this->_multiFetch("thread:" . $comment['id']);
				$curr[$comment['id']] = $this->_processComments($data);
			}
			$curr[$comment['parentId']][] = $comment;
		}	
		return $curr;
	}
	/**
	 * Returns the comments according to a list of IDs stored in a Redis List
	 * @param String $keyName the Redis List key name
	 * @return array
	 */
	private function _multiFetch($keyName) {
		$commentList = $this->_redis->lRange($keyName, 0, -1);

		$this->_redis->multi();
		foreach($commentList as $commentId) {
			$this->_redis->hGetAll("comment:" . $commentId);
		}
		return $this->_redis->exec();
	}
	/**
	 * Generates a unique ID for the comment
	 * return String
	 */
	private function _getCommentId() {
		return sprintf( '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
    	    mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ),
	        mt_rand( 0, 0xffff ),
	        mt_rand( 0, 0x0fff ) | 0x4000,
	        mt_rand( 0, 0x3fff ) | 0x8000,
    	    mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff )
		);
		//Could also be
		//return $this->_redis->incr("comments:id:next");
	}
}

example.php

<?php
include "Comments.php";

$comments = new Comments();

$id = $comments->save(1, "Redis is awesome!", "Mikushi", 42);
	$otherId = $comments->save(1, "i know!", "Asiendra", 43, $id);
		$comments->save(1, "yeeha!", "Mikushi", 42, $otherId);
		$comments->save(1, "mehehehe!", "Pythian", 44, $otherId);
	$comments->save(1, "I'm jaleous!", "MongoDB", 45, $id);
	$comments->save(1, "Me too!", "Memcached", 45, $id);
$comments->save(1, "Redis is the shit!", "Me", 46);
$comments->save(1, "Correction, Redis is The shit!", "OtherMe", 47);


$myComments = $comments->getComments(1);

printComments($myComments[1], 0, $myComments);

function printComments($thread, $margin, $container) {
	foreach($thread as $comment) {
		echo "<div style='border: 1px solid black; padding: 4px; margin-left: ".$margin."px'>" . $comment['username'] . " - " . $comment['content'] . "</div>";
		if($comment['hasChildren'] === "1") {
			printComments($container[$comment['id']][$comment['id']], $margin+20, $container[$comment['id']]);
		}
	}
}

So, how would you go about deleting a node from the tree? (Especially if it has children).

I made a Ruby version based on this Gist. Here it is: https://gist.github.com/2766062

I made a C# version based on this Gist. Here it is: https://gist.github.com/2788831