Monday, April 16, 2007

An easy way to add (web 2.0 like) tags to your posts

One of the features that is closely linked to the web 2.0 developments is the use of Tags. Tags are short phrases (/words) that describe the article they accompany. Tags are great for categorizing posts and give the reader of an article information on it's subject instantly.

You see, for Tags to be effective it would be best to minimize the variety being used. If all tags concerning programming have a tag 'programming' attached to them, we could use that tag to effectively categorize those posts. Using standard tags for posts helps us create a more structured and better organized category system. The problem however is that you can't remember all the tags you already use and you probably don't have enough room (or want for that matter) to show all the tags in a row.

Using however this problem is solved very easily! First of all, if you didn't know this already, Scripaculous is an open source Javascript framework. It used the Prototype framework and it provided many graphical effects and other powerful tools to it's users. One of the things it offers is an Autocompletion class, which we are going to use to make our lives a lot easier. Basically autocompletion presents matching options while the user is typing. The user can click the options (or use his keyboard) to select an option after which the text is inserted in his input field. Go to this Scriptaculous demonstration to see what I'm talking about.

First of all we need a database that contains the tags. This database must at least contain these fields:
- id (int, primary key, auto_increment)
- tag (varchar, unique)

Then we need a table to link tags to posts:
- tag_id (int)
- post_id (int)

Next, let's set up the input page. First of all we need an INPUT field, e.g.:
<input name="tags" id="tags" value="" style="width: 300px;" type="text">

Next we need an invisible DIV that Scriptaculous will use to show it's autocompletion results, e.g.:

<div id="auto_complete" style="display: none;"></div>

Now on to the Javascript!
For the sake of easy testing, let's add a local array containing the tags that are already used on the website (the tags the autocompleter will use):
var tags = new Array('news', 'websites', 'links', 'programming', 'php', 'mysql', 'apache', 'games', 'hardware', 'holiday', 'business', 'ICT', 'music');

Be sure to add that inside a Javascript block!

Here comes the magic! Below the form field containing the tags, add the following Javascript function (inside a javascript block:
new Autocompleter.Local('tags', 'auto_complete', tags, {});

This function will add the autocompleter. It will use the INPUT field 'tags', fill the DIV 'auto_complete' with results and use Javascript array 'tags' as it's source. The {} at the end signify the options array (empty for now).

The above works! However there is a small problem with it.. It will only allow you to add one tag! After that, autocompletion won't work.. Luckily, Scriptaculous can fix that! In the empty brackets ({}) at the end, add the following: tokens: ','

Or make it like this:
new Autocompleter.Local('tags', 'auto_complete', tags,
tokens: ','

Now you can add multiple tags and seperate them using commas! How neat is that! You can also set more options (for instance partial searching, minimum characters for autocomplete to start, etc), which are described here.

Of course it's also possible to load the autocompletion tags using Ajax. I think however it would be better to render the tags array using PHP at page load, because of performance (each Ajax request takes time, while the tags won't change..).

Click here to view my demonstration page for the above!

Next is the PHP part!

I won't go into much detail here.. This part basically requires 2 steps:

  1. Split up the tags;
  2. Save each one. If they already exist in your table, only add a link from the new post to the tag, if they didn't exist add the new tag and link the post to it.
Splitting up requires a small 'heads-up': scriptaculous will allow whitespace after the seperating comma, so you need to watch out for that aswell. Here's how:

// Strips whitespace at the beginning of a string
$_POST['tags'] = ltrim($_POST['tags']);

// Splits up the tags
$tags = preg_split('/[ \t]*,[ \t]*/', $_POST['tags']);

Now all you need to to is loop through $tags and store the tags (as described in point #2). Make sure you first check if the tag already exists! If it does, only store the link from this post to the tag! If it doesn't, add the tag, then get it's id (mysql_insert_id()) and then store the post->tag link.

On great thing to do with tags is create a (Web 2.0) tag cloud!

Also be sure to check out my demonstration for the above!

Happy web 2.0'ing!

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