Categories and CategoryNodes API Guide

From Joomla! Documentation


The Joomla Categories and CategoryNode APIs enable you to access details of Joomla categories. The diagram below illustrates how the Joomla category classes relate to the database structures.

Categories diagram

The Joomla Categories table is split into "partitions", one partition for each component which uses categories. (Here "partitions" is used in a loose sense, not related to the technical term "database partition" for example). Within each partition the category records are held within a tree structure, but always associated with the same component – for example, you can't have a com_content category which has as a parent a com_contact category. At the root of the tree is a single system root node, which is the parent of all the top-level category records of the components.

Each component record which is associated with a category holds the id of the category record (as a foreign key), with all the category attributes being held in the category record within the Categories table. (Shown in the diagram using the example of com_contact).

There are 2 Joomla classes (shown in yellow) which provide APIs for accessing category data:

  1. Categories – This relates to the partition within the Categories table. You must first of all specify which partition you want to access by creating a Categories object and passing the name of the component as a parameter to the constructor.
  2. CategoryNode – This relates to an individual Category record. Once you have the Categories object you can get access to the CategoryNode objects within that partition.

In your code you can access the category data for several components, through creating several Categories instances, one for each component/partition.


To get access to the set of categories for com_content use:

use Joomla\CMS\Categories\Categories;
$extension = "content";
$categories = Categories::getInstance($extension);
// The above replaces the older format $categories = JCategories::getInstance($extension);
$categoryNodes = $categories->get(12);   // returns the category node for category with id=12

Note that you don't have the usual "com_" prefix in the extension.

You can provide an associative array of options as a second parameter to the Categories static getInstance() method. The keys of this array are:

  • "access" – if this is true (or some value which equates to PHP true) then only categories which the current user has access to view will be returned. If false then all categories will be returned, regardless of whether the current user has access to view them or not. The default is true.
  • "published" – if this is 1 (integer one) then only categories which have a published state of 1 (ie 'published') will be returned. Otherwise categories of any state will be returned. The default is 1, meaning that only 'published' categories will be returned.
  • "countitems" – if this is 1 (integer one) then when categories are returned Joomla will determine for each category record how many of the extension records are associated with that category (the default is not to count the items). To do this, Joomla will do a SQL JOIN with the extension table, WHERE the category id field in that table matches, and COUNTing the instances of a "key" field in that table. Joomla needs to know what these tables and fields are called, and these can be provided in the array options below.
  • "table" – the name of the extension table. There is no default, so you must supply this if you're using "countitems".
  • "field" – the name of the field in the extension table which holds the category id (default "catid")
  • "key" – the name of the key field in the extension table over which the SQL COUNT is performed (default 'id').
  • "statefield" – the name of the field in the extension table which holds the published status of the record (default 'state'). If Joomla is returning only published categories (as determined by the "published" option described above) then it will count over just published items in the extension table as well. (Note that the equivalent is NOT done for "access" – any Access field in the extension table is ignored).


$categories = Categories::getInstance("content", array("access" => false, "published" => 0));

Category nodes returned will not be restricted by Access or the Published state.

$categories = Categories::getInstance("helloworld", array("countitems" => 1, "table" => "helloworld", "statefield" => "published"));

Category nodes of the "helloworld" component will include the number of associated records in the "helloworld" table, where the published state is held in a field called "published".

The Categories get() method takes as its first parameter the id of the category record to be read from the database and returns to the caller the corresponding CategoryNode object. If no id is given, then the method returns the CategoryNode object relating to the system ROOT record at the very top of the category tree in the database.

The get() functionality actually reads from the database all the ascendents of the requested category record up to the category root record (which enables the Category Path described below to be determined), as well as all the descendants of the requested category record. It then stores these locally so that subsequent calls to obtain data for any of those children can be served by returning the data from this cache rather than performing another query on the database.

However, if the second parameter $forceload is set to true, then it will service the request by querying the database again, rather than using the cached records.

In a multilanguage site the categories returned will be restricted to those of the current language or language * (for all). Similarly, any counting of items in the extension table will be restricted to those of the current language or language *, and Joomla will assume that the language is stored in field called "language" (you can't override what this language field is called).

CategoryNode Properties[edit]

The object from a call to the Categories get($id) method will be a CategoryNode object relating to the category with id $id. If you called get() using the default of 'root' then you will have to make a subsequent call to getChildren() to get an array of CategoryNode objects for the extension you want, eg:

use Joomla\CMS\Categories\Categories;
use Joomla\CMS\Categories\CategoryNode;

$categories = Categories::getInstance("content");
$rootNode = $categories->get();   
$categoryNodes = $rootNode->getChildren();

Once you have a CategoryNode object you can access the properties of this object as defined in the API definition, and these mostly relate closely to the category attributes visible in the Joomla admin forms. Properties where the meaning is fairly clear are not described below, but below is a list of those where the meaning may not be totally apparent.

  • asset_id – where the administrator has defined ACLs for the individual category, then this is the id of the record in the asset table where these ACLs are stored.
  • parent_id, lft, rgt, level – these fields relate to the category's position in the category tree, which is implemented using the Nested Set model. The lft and rgt values are implemented as required by the model, the parent_id is the id of the parent record in the category table (NOT in the asset table – this is a typo in the Joomla code), and the level is 0 for the root node, 1 for those records whose parent is the root node, 2 for the next level of descendants, etc.
  • extension – this time the "com_" prefix is present
  • numitems – the number of records in the extension table which are associated with this category
  • childrennumitems – this isn't set – don't try to use it!
  • slug – this is what Joomla has traditionally displayed as part of the URL when SEF URLs are displayed. It's of the form id:alias, for example 3:uncategorised.
  • assets – this isn't set – don't try to use it!

CategoryNode get Methods[edit]

A number of the CategoryNode get methods enable you to access other CategoryNode objects in the tree:

  • getChildren(boolean $recursive = false) returns an array of the immediate children, or an array of all the descendants if $recursive = true.
  • getParent() returns the parent CategoryNode
  • getSibling(boolean $right = true) returns the sibling CategoryNode to the right, or to the left if $right = false.

A number of the get methods return properties of the CategoryNode object

  • getAuthor(boolean $modified_user = false) returns the User object associated with the user who created the category, or the user who last modified the user if $modified_user = true
  • getMetadata() returns a Joomla Registry object containing the category metadata (json structure)
  • getParams() returns a Joomla Registry object containing the category params (json structure)
  • getNumItems(boolean $recursive = false) returns the number of records in the extension table which are related to this category. If $recursive = true then it's the total number of records associated with this category and all of this category's descendants.
  • getPath() returns an array of the slugs going from the root of the category tree down the tree to this category. For example, if this category has id 9 and alias "dog", it's parent has id 6 and alias "mammal", and grandparent (immediately below the root) has id 3 and alias "animal" then getPath() will return array(3 => "3:animal", 6 => "6:mammal", 9 => "9:dog").

Note that hasParent() includes the parent being the root node, so that a call to this method will always return true unless you're calling it on the root node.

CategoryNode set Methods[edit]

There are a number of set methods of the CategoryNode API, but these are primarily used by the Joomla category functionality to set up the CategoryNode objects, based on data retrieved from the database. Calling one of these does not persist the data to the database, eg you can't use setParent() to reparent a category record under a different category parent in the database.

Sample Module Code[edit]

Below is the code for a simple Joomla module which you can install and run to demonstrate use of the Categories and CategoryNode API functionality. If you are unsure about development and installing a Joomla module then following the tutorial at Creating a simple module will help.

In a folder mod_sample_categories create the following 2 files:


<?xml version="1.0" encoding="utf-8"?>
<extension type="module" version="3.1" client="site" method="upgrade">
    <name>Categories demo</name>
    <description>Code demonstrating use of Joomla APIs related to Categories</description>
        <filename module="mod_sample_categories">mod_sample_categories.php</filename>


defined('_JEXEC') or die('Restricted Access');

use Joomla\CMS\Factory;
use Joomla\CMS\Categories\Categories;
use Joomla\CMS\Categories\CategoryNode;

$app = Factory::getApplication();
$input = $app->input;
$ext = $input->get('categoryextension', "Content", "STRING");
$tab = $input->get('categorytable', "Content", "STRING");
echo "Getting {$ext} categories and using {$tab} table<br>";
echo "-------------<br>";

$categories = Categories::getInstance($ext, array("table" => "Content", "countItems" => 1, "access" => false));

$cat0 = $categories->get('root');

$cats = $cat0->getChildren(true);
foreach ($cats as $cat)
	echo "Category {$cat->id}, title: {$cat->title}<br>";
	echo "Level: {$cat->level}, parent id: {$cat->parent_id}<br>";
	echo "Numitems {$cat->getNumitems()}, including descendants: {$cat->getNumitems(true)}<br>";
	echo "-------------<br>";

$ext2 = $input->get('option', "", "STRING");
$catid = $input->get('catid', 0, "INT");
$view = $input->get('view', "", "STRING");
$id = $input->get('id', 0, "INT");
if ($ext2 && (strtolower(substr($ext2, 0, 4)) == "com_") && ($catid || (strtolower($view) == "category" && $id)))
	$ext2 = substr($ext2, 4);
	$categories2 = Categories::getInstance($ext2, array("access" => false));
	$categoryId = $catid ? $catid : $id; 
	echo "<br>Getting $ext2 category $categoryId<br>";
	$cat2 = $categories2->get($categoryId);
	if ($cat2)
		echo "Category {$cat2->id}, title: {$cat2->title}<br>";

Zip up the mod_sample_categories directory to create

Within your Joomla administrator go to Install Extensions and via the Upload Package File tab select this zip file to install this sample categories module.

Make this module visible by editing it (click on it within the Modules page) then:

  1. making its status Published
  2. selecting a position on the page for it to be shown
  3. on the menu assignment tab specify the pages it should appear on

When you visit a site web page then you should see the module in your selected position, and it should show the set of com_content categories in the database and for each category:

  • the id and title
  • the level in the category tree and the id of the parent
  • the number of articles which have this category set, and the number of articles which have this category or any of the category's descendants
  • a var_dump of the category getPath() return value.

You can get categories for other components by adding the parameters categoryextension and categorytable to the URL, eg ...&categoryextension=contact&categorytable=contact_details to get com_contact categories. Note that if you're trying to get the categories of a component which isn't one of the core Joomla components, then you may need to supply the component field names etc within the options to the Categories::getInstance() call, as described above.

The code also tries to guess if the page displayed relates to a category, by checking if there's a catid parameter in the URL, or if the view parameter is set to 'category'. In this case it shows the id and title of the associated category. Obviously this may not work correctly in all cases.