Adding a statically-linked syndication feed, a feed that is the same no matter where on the site you are, is a cinch with symfony, but what about dynamically linked syndication feeds? Let’s say we’re building the latest and greatest Web 2.0 app, there’s going to be hundreds of RSS feeds, not just the most recent items. We’ll want the latest comments to a post, the favorite things of a website member and it all has to be feed enabled. Sure, we can slap a link to the RSS feed and call it a day, but let’s go a step further and stick it in the <head/> area as well. That way when someone clicks on the RSS icon in their browser, or adds a web page to Bloglines those extra feeds can be found.
Expanding your head
A typical layout.php for a symfony app will have a <head/> section like this:
<head>
<?php echo include_http_metas() ?>
<?php echo include_metas() ?>
<?php echo include_title() ?>
<?php echo auto_discovery_link_tag('rss', 'feed/latest')?>
<?php echo auto_discovery_link_tag('rss', '@feed_latest_georss',
array('title' => 'Latest Restaurants\' Locations (GeoRSS)' ))?>
<?php echo include_feeds() ?><!-- this is the custom feed includer -->
<link rel="shortcut icon" href="/favicon.ico" />
</head>
Since this is in the reviewsby.us layout.php, the latest feed and the latest GeoRSS feed (which we developed in this article) will show up on every page. So for example, if you use FireFox, you can subscribe to either link when you click on the orange feed icon (
) in the URL bar no matter where you are in the web-application.
To expand this to allow for multiple feeds, we need to include <?php echo include_feeds() ?> (before or after the auto_discovery_link_tag calls makes the most sense).
Making the Feed Helper
Let’s created a FeedHelper.php to put the include_feeds() function (don’t forget to add use_helper('Feed') to your layout.php).
The function looks like this:
function include_feeds()
{
$type = 'rss';
$already_seen = array();
foreach (sfContext::getInstance()->getRequest()->getAttributeHolder()->getAll('helper/asset/auto/feed') as $files)
{
if (!is_array($files))
{
$files = array($files);
}
foreach ($files as $file)
{
if (isset($already_seen[$file])) continue;
$already_seen[$file] = 1;
echo tag('link', array('rel' => 'alternate', 'type' => 'application/'.$type.'+xml', 'title' => ucfirst($type), 'href' => url_for($file, true)));
}
}
}
The function is doing what the deprecated include_javascripts and include_stylesheets functions did, just with syndication feeds. Also note, I stuck to just using RSS feeds. This function can no doubt be extended to Atom or other feed types, but for my purposes it was unnecessary1.
Dynamically setting the feeds
In the reviewsby.us site, the menu items are tagged. There’s tags for chicken, indian and bread for example. Each of them are to have an associated GeoRSS feed as described in a previous tutorial. I built our tagging system similar to Askeet. So in our tag module I created a function in the corresponding actions.class.php:
public function addFeed($feed)
{
$this->getRequest()->setAttribute($feed, $feed, 'helper/asset/auto/feed');
}
This sets the attribute that include_feeds() pulls from. Here $feed is simply the route to our feed. So in our executeShow() I just make a call to $this->addFeed('@feed_tag_georss?tag=' . $tag). We’re done.
We can now go to any of our tagged pages. Let’s try chicken and see that we can subscribe to a GeoRSS feed of restaurants serving dishes tagged as chicken.
Slight problem. The title attribute of the generated link tags are always Rss. That can be mildly unusable.
Throwing feed titles into the mix
Let’s change our addFeed() to allow for a second parameter, a title and have it store both the route and the title in the request attribute:
public function addFeed($feed, $title = null)
{
$feedArray = array('url' => $feed, 'title' => $title);
$this->getRequest()->setAttribute($feed, $feedArray, 'helper/asset/auto/feed');
}
We’ll also need to adapt the include_feeds to appropriately accommodate associative arrays:
function include_feeds()
{
$type = 'rss';
$already_seen = array();
foreach (sfContext::getInstance()->getRequest()->getAttributeHolder()->getAll('helper/asset/auto/feed') as $feeds)
{
if (!is_array($feeds) || is_associative($feeds))
{
$feeds = array($feeds);
}
foreach ($feeds as $feed)
{
if (is_array($feed)) {
$file = $feed['url'];
$title = empty($feed['title']) ? $type : $feed['title'];
} else {
$file = $feed;
$title = $type;
}
if (isset($already_seen[$file])) continue;
$already_seen[$file] = 1;
echo tag('link', array('rel' => 'alternate', 'type' => 'application/'.$type.'+xml', 'title' => $title, 'href' => url_for($file, true)));
}
}
}
Note, there’s a function is_associative(). It’s a custom function that we can place in another helper:
function is_associative($array)
{
if (!is_array($array) || empty($array)) return false;
$keys = array_keys($array);
return array_keys($keys) !== $keys;
}
It’s a clever way of determining if a function is an associative array or not.
Conclusion
It looks like our GeoRSS feeds are on all our tag pages. Now we can take our favorite items labeled as Indian food and easily add the URL to a service like Bloglines and have it keep us up to date on new Indian dishes. This was simple, especially when much of the work was taken care of by the framework.
- Most clients support RSS so unless there is a compelling need to use Atom or another format, then keeping it down to one choice is always your best bet. ↩