Building an SEF URL

The building of an SEF URL is initiated with a call like:

use Joomla\CMS\Router\Route;
...
$url = Route::_('index.php?option=com_content&view=article&id=21&catid=50&lang=en-GB');

Here we provide the query parameters in the call, and it's the router's job to generate the SEF URL, which might end up something like:

http://localhost/joom/index.php/en/mountains/50-alps/21-mont-blanc

There are 2 main stages in generating this URL:

1. A preprocess stage to identify the menuitem upon which to base this URL, and
2. A build stage where the segments are built

Plus a tidy-up at the end.

Preprocess Stage

The preprocess stage falls within the remit of the component router. The Joomla Site Router uses the option parameter in the Route::_() call to identify the component (com_content in this example). It then looks to call the preprocess method of the component router:

public function preprocess($query)

The query parameters are passed as an associative array rather than as a string, ie like:

$query = array('view' => 'article', 'id' => '21', ...)

It's the job of the component router preprocess function to identify the menuitem to use and set it within the $query array:

$query['Itemid'] = 13;
return $query;

The core Joomla components generally don't explicitly provide the preprocess() function within their component router, but instead specify RouterView configurations - this is something described in the next section - and then it is the Site Router itself which provides the preprocess() function, and we'll consider how it does this for com_content.

In this case the Site Router finds all the menuitems on the site which relate to com_content and chooses one of them to base the SEF URL upon. Note that the set of menuitems will include those which are hidden, but not those which are unpublished.

How does the router know which one of these menuitems to select? Actually, the logic for selecting the menuitem has changed over a number of releases, causing a few Joomla Stack Exchange questions to be raised on the topic. As a general guide, it seems to be based on whatever rule is present first within the RouterView rules.

Note that you can specify the menuitem id (ie Itemid) in the Route::_() call:

$url = Route::_('index.php?option=com_content&view=article&id=21&Itemid=6); ?>

but the router may well ignore this and base the URL on a completely different menuitem.

However, the flexibility of Joomla is such that if you don't like the way it selects the menuitem then you can write a plugin to override the default functionality with your own defined algorithm, as shown in system plugin router rules.

The selected menuitem provides the starting segment for our SEF URL, based on the menuitem's Alias field. If the menuitem is in a submenu, then the aliases of the parent menuitems going up through the menu tree are prepended as segments also - this is actually the route property of the menuitem, described in Menus and Menuitems.

Let's assume the menuitem selected is a top-level menuitem, points to an article category list, and has alias 'mountains'. Our segments array will then have a single element:

$segments = array('mountains')

What happens if there aren't any menuitems on the site which relate to the option specified in the Route::_() call?

In this case the router will base the SEF URL on the home menuitem (for that language if it's a multilingual site). It will then add on segments which point to the component etc to use. For example, if the component is com_contact you could end up with segments something like:

/en/component/contact/contact/me?Itemid=1

This is a bad situation and to be avoided at all costs! The link (if it works at all!) will end up with the home page formatting and modules.

The situation can easily be avoided by specifying a hidden menuitem which is associated with that component. However, extension developers don't necessarily have control over how administrators build their menu structures.

Build Stage

The build stage is largely within the remit of the component router, and the Site Router looks to call the build method of the component router:

public function build(&$query)

The query parameters are passed as an associative array and should now have the menuitem Itemid set, eg:

$query = array('Itemid' => '13', 'view' => 'article', 'id' => '21',  catid => '50', ...)

The job of the component router build function is to generate the array of segments for the SEF URL, based on the query parameters passed it. It should return the array of segments and unset any query parameters which are used:

$segments = array('50-alps', '21-mont-blanc');
unset($query['view']);
unset($query['id']);
unset($query['catid']);
return $segments;

If you don't unset some of the query parameters then they're added into the URL (in the query part of the URL), eg:

http://localhost/joom/index.php/en/mountains/50-alps/21-mont-blanc?view=article&id=21

The component router has the freedom to decide what segments it's going to set. It just has to be able to parse these segments when the URL is clicked by the user.

Traditionally Joomla has set the segment to be of the form id:alias of the item, but the id part can be removed (leaving just the alias as the segment) by setting (for com_content) the Global Configuration: Articles / Integration / Routing Remove IDs from URLs option. (Similarly for Contacts). The advantage of the id:alias format is that a database lookup isn't required when parsing the incoming URL. If you just use the alias format on your component then ensure that there's an index on your alias field in the database.

Generally if the menuitem points to a single item (like a single article, or a single contact) then it can just create a segment which is the id:alias (or just alias) of that item.

If the menuitem points to a category list of items then it should provide the category id:alias, and it's common to include the parent categories up the category tree. This can be easily found using the CategoryNode getPath() method, described in CategoryNode get Methods. (If you're not using ids in the segments then remember that category aliases don't have to be unique throughout a Joomla instance; they just have to be unique across the categories at the same level in the hierarchy. Hence the category path is needed.)

In our example we've assumed that the menuitem relates to a category list, and we provide as segments:

• the id-alias ('50-alps') of the item's category (which we've assumed is at the top level of the category tree)
• the id-alias of the item ('21-mont-blanc').

Including the 'mountains' segment which was found in the preprocess function, we now have 3 segments:

/mountains/50-alps/21-mont-blanc

Remainder of URL

By this stage all the hard work of generating the SEF URL has been done. All that remains is to add the language segment (again done by the Language Filter plugin on a multilingual site), and the domain and entry point (index.php) if required.