Almost every website divides its content into categories. Joomla offers this useful feature as well. The current part of the tutorial shows you how to ideally integrate categories into a Joomla component. Don't reinvent the wheel yourself. Use what Joomla offers you.

Categories are a way of organising content in Joomla A category contains posts and other categories. A post can only be in one category. If a category is contained in another, it is a subcategory of the category.

For impatient people: View the changed program code in the Diff View[^] and copy these changes into your development version.

Step by step

New files


We store the data in the database that is necessary to classify an element into a category. Therefore, in case of an update, it is important to add a column to the database. To do this, we create the file administrator/components/com_foos/sql/updates/mysql/12.0.0.sql and enter the necessary SQL statement in it. We choose the name because we are currently working on version 12 of our extension.


<!-- -->

ALTER TABLE `#__foos_details` ADD COLUMN  `catid` int(11) NOT NULL DEFAULT 0 AFTER `alias`;

ALTER TABLE `#__foos_details` ADD KEY `idx_catid` (`catid`);

Modified files

administrator/components/com_foos/ access.xml

The entries in the file access.xml marked below with a plus sign are necessary to set permissions for the categories. The new code causes the display of a tab for setting user permissions per category in the administration area.


 		<action name="core.edit" title="JACTION_EDIT" />
 		<action name="core.edit.state" title="JACTION_EDITSTATE" />
 		<action name="core.edit.own" title="JACTION_EDITOWN" />
		<action name="core.edit.value" title="JACTION_EDITVALUE" />
	<section name="category">
		<action name="core.create" title="JACTION_CREATE" />
		<action name="core.delete" title="JACTION_DELETE" />
		<action name="core.edit" title="JACTION_EDIT" />
		<action name="core.edit.state" title="JACTION_EDITSTATE" />
		<action name="core.edit.own" title="JACTION_EDITOWN" />


The <menu link="option=com_categories&amp;extension=com_foos" entry causes a menu item to be added in the administration area menu for editing the category.


 		<menu view="foos">COM_FOOS</menu>
 			<menu link="option=com_foos">COM_FOOS</menu>
			<menu link="option=com_categories&amp;extension=com_foos">JCATEGORY</menu>
 		<files folder="administrator/components/com_foos">

administrator/components/com_foos/ forms/foo.xml

We add a selection field with matching categories to the form used to create a Foo item. We use the Joomla own field categoryedit for this. Note the line extension="com_foos". This ensures that only categories belonging to the component com_foos are displayed.






To ensure that a category already exists at the beginning, we add the script that is called during the installation. Using the install method, we create a category with the title Uncategorised for the component during a new installation. We store these directly in the database. To be able to specify a user as the creator of the category, we request the ID of the administrator in the getAdminId() method.


  * @license     GNU General Public License version 2 or later; see LICENSE.txt
 \defined('_JEXEC') or die;

use Joomla\CMS\Application\ApplicationHelper;
use Joomla\CMS\Factory;
 use Joomla\CMS\Installer\InstallerAdapter;
 use Joomla\CMS\Language\Text;
 use Joomla\CMS\Log\Log;
use Joomla\CMS\Table\Table;

  * Script file of Foo Component


		$db = Factory::getDbo();
		$alias   = ApplicationHelper::stringURLSafe('FooUncategorised');

		// Initialize a new category.
		$category = Table::getInstance('Category');

		$data = array(
			'extension' => 'com_foos',
			'title' => 'FooUncategorised',
			'alias' => $alias . '(en-GB)',
			'description' => '',
			'published' => 1,
			'access' => 1,
			'params' => '{"target":"","image":""}',
			'metadesc' => '',
			'metakey' => '',
			'metadata' => '{"page_title":"","author":"","robots":""}',
			'created_time' => Factory::getDate()->toSql(),
			'created_user_id' => (int) $this->getAdminId(),
			'language' => 'en-GB',
			'rules' => array(),
			'parent_id' => 1,

		$category->setLocation(1, 'last-child');

		// Bind the data to the table
		if (!$category->bind($data))
			return false;

		// Check to make sure our data is valid.
		if (!$category->check())
			return false;

		// Store the category.
		if (!$category->store(true))
			return false;

 		return true;

 		return true;

	private function getAdminId()
		$db    = Factory::getDbo();
		$query = $db->getQuery(true);

		// Select the admin user ID
			->select($db->quoteName('u') . '.' . $db->quoteName('id'))
			->from($db->quoteName('#__users', 'u'))
				$db->quoteName('#__user_usergroup_map', 'map')
				. ' ON ' . $db->quoteName('map') . '.' . $db->quoteName('user_id')
				. ' = ' . $db->quoteName('u') . '.' . $db->quoteName('id')
				$db->quoteName('#__usergroups', 'g')
				. ' ON ' . $db->quoteName('map') . '.' . $db->quoteName('group_id')
				. ' = ' . $db->quoteName('g') . '.' . $db->quoteName('id')
				$db->quoteName('g') . '.' . $db->quoteName('title')
				. ' = ' . $db->quote('Super Users')

		$id = $db->loadResult();

		if (!$id || $id instanceof \Exception)
			return false;

		return $id;

administrator/components/com_foos/ services/provider.php

In the service provider we register the interface CategoryFactoryInterface. It is not necessary to create CategoryFactory Interface by yourself. We use the Joomla own functions.


 \defined('_JEXEC') or die;

use Joomla\CMS\Categories\CategoryFactoryInterface;
 use Joomla\CMS\Dispatcher\ComponentDispatcherFactoryInterface;
 use Joomla\CMS\Extension\ComponentInterface;
 use Joomla\CMS\Extension\Service\Provider\CategoryFactory;


 				return $component;


In order to create the table column in which the category of a Foo element is stored during a new installation, we add the necessary SQL command in the SQL file that is called during the installation.


 ALTER TABLE `#__foos_details` ADD COLUMN  `access` int(10) unsigned NOT NULL DEFAULT 0 AFTER `alias`;

 ALTER TABLE `#__foos_details` ADD KEY `idx_access` (`access`);

ALTER TABLE `#__foos_details` ADD COLUMN  `catid` int(11) NOT NULL DEFAULT 0 AFTER `alias`;

administrator/components/com_foos/ src/Extension/FoosComponent.php

Additionally, implementations are required in the component class to use Joomla's own functions. The method countItems is necessary so that an overview of assigned items appears in the category view. The method getTableNameForSection ensures that the correct database table is always queried.


 use Joomla\CMS\HTML\HTMLRegistryAwareTrait;
 use FooNamespace\Component\Foos\Administrator\Service\HTML\AdministratorService;
 use Psr\Container\ContainerInterface;
use Joomla\CMS\Helper\ContentHelper;

  * Component class for com_foos

 		$this->getRegistry()->register('foosadministrator', new AdministratorService);

	public function countItems(array $items, string $section)
			$config = (object) array(
				'related_tbl'   => $this->getTableNameForSection($section),
				'state_col'     => 'published',
				'group_col'     => 'catid',
				'relation_type' => 'category_or_group',

			ContentHelper::countRelations($items, $config);
		catch (\Exception $e)
			// Ignore it

	protected function getTableNameForSection(string $section = null)
		return ($section === 'category' ? 'categories' : 'foos_details');


administrator/components/com_foos/ src/Model/FoosModel.php](

In the model we add to the database query the table where Joomla stores categories. Thus, in the administration area, when a category is selected, only the elements belonging to it are displayed.


 		// Select the required fields from the table.
			$db->quoteName(array('', '', 'a.alias', 'a.access'))
			$db->quoteName(array('', '', 'a.alias', 'a.access', 'a.catid'))

 		$query->from($db->quoteName('#__foos_details', 'a'));

 				$db->quoteName('#__viewlevels', 'ag') . ' ON ' . $db->quoteName('') . ' = ' . $db->quoteName('a.access')

		// Join over the categories.
		$query->select($db->quoteName('c.title', 'category_title'))
				$db->quoteName('#__categories', 'c') . ' ON ' . $db->quoteName('') . ' = ' . $db->quoteName('a.catid')

 		return $query;

administrator/components/com_foos/ tmpl/foo/edit.php

We add the category field to the form for editing an element. It is rendered using the information in the XML form administrator/components/com_foos/forms/foo.xml, which we worked on earlier in this chapter.


 	<?php echo $this->getForm()->renderField('name'); ?>
 	<?php echo $this->getForm()->renderField('alias'); ?>
 	<?php echo $this->getForm()->renderField('access'); ?>
	<?php echo $this->getForm()->renderField('catid'); ?>
 	<input type="hidden" name="task" value="">
 	<?php echo HTMLHelper::_('form.token'); ?>

administrator/components/com_foos/ tmpl/foos/default.php

In the overview table of the view in the backend, we add a column for displaying the category.


		<a class="hasTooltip" href="<?php echo Route::_('index.php?option=com_foos&task=foo.edit&id=' . (int) $item->id); ?>" title="<?php echo Text::_('JACTION_EDIT'); ?> <?php echo $this->escape(addslashes($item->name)); ?>">
			<?php echo $editIcon; ?><?php echo $this->escape($item->name); ?></a>

		<div class="small">
			<?php echo Text::_('JCATEGORY') . ': ' . $this->escape($item->category_title); ?>
	<td class="small d-none d-md-table-cell">
		<?php echo $item->access_level; ?>

The categories help you to display your data in a structured way in the frontend. We will create the frontend views in the further course of this tutorial.

Test your Joomla component

  1. install your component in Joomla version 4 to test it: Copy the files in the administrator folder to the administrator folder of your Joomla 4 installation. Install your component as described in part one, after copying all files. Joomla will update the database for you during the installation. On the right-hand side of the table is an overview that lists how many elements are published or unpublished. This does not work yet. We will work on publishing and unpublishing in the next part.

  2. Open the view of your component in the administration area.

  3. in the sidebar you will see a new menu item. This offers you everything you need to create and edit the categories of your component.

Joomla Category Menu Item

  1. next open an element. Make sure that it is possible to assign a category to it.

Joomla Assign Category

  1. make sure that the foo specific categories do not appear in other components, for example in com_contact.