Categories

Most hubs need one or two article categories, and a good many need none. A category earns its place when a group of pages belongs together — an About section with an overview, a contact page and an acknowledgements page — or when you want the pages' addresses to share a prefix. A single About page reached through a menu item needs no category at all: leave it in Uncategorised and nothing is lost. Creating a category tree before there is content to put in it is the commonest way a manager makes a small hub feel complicated.

There is one thing categories do that nothing else does, and it is worth the trouble on a bigger hub: a category's state and access level apply to everything filed in it. Unpublishing one category takes a whole branch of the site down in a single save, and republishing it brings every page back in whatever state it was already in. That is covered under States and permissions below.

The Category Manager is one screen that several components borrow. Articles, user notes, knowledge base articles and events all file their content in categories, and all four open the same component, com_categories, to create and edit them. This chapter is for the administrator who has arrived at that screen from any of those places and wants to know what it does, what the categories they are looking at belong to, and why the screen looks identical no matter where they came from.

com_categories has no entry of its own in the Components menu, and that is deliberate — the migration that registers the component says so and passes false where it would otherwise ask for a menu item. You always reach the Category Manager through the component whose categories you want.

One manager, four extensions

Every category row carries an extension column naming the component it belongs to. The screen is scoped by an extension parameter in the URL that matches it. Four components ship with a hub and open the manager:

Extension	Where you open it from	What the categories are for
com_content	Content → Category Manager, the Categories submenu entry on the Article Manager, and the Category Manager icon on the control panel	Filing articles, and building their URLs
com_members	Users → User Note Categories, and Note Categories under Users → Members → Notes	Filing user notes
com_kb	The Categories submenu entry in the Knowledge Base	Grouping knowledge base articles
com_events	The Categories submenu entry in Events	Grouping events

Each of those links is the same URL with one word changed:

/administrator/index.php?option=com_categories&extension=com_content
/administrator/index.php?option=com_categories&extension=com_members
/administrator/index.php?option=com_categories&extension=com_kb
/administrator/index.php?option=com_categories&extension=com_events

The categories are not shared between them. A category created under com_content is invisible to notes, to the knowledge base and to events, and the list, the Parent menu and the batch panel are all filtered to one extension at a time. What is shared is the screen, the database table and the tree they all hang from.

The page title says which extension you are in: Category Manager: Articles for com_content, Category Manager: Members, Category Manager: Knowledge Base, Category Manager: Events. The name comes from the owning component's language file, so if that file is not loaded the title falls back to the raw com_… string.

The submenu disappears

When you open the Category Manager, the owning component's submenu is not drawn by that component any more, so com_categories tries to rebuild it: it looks for admin/helpers/<name>.php in the owning component, expects a class called <Name>Helper with an addSubmenu method, and calls it.

Only com_members has one. Open the Category Manager from Articles, the Knowledge Base or Events and you lose that component's submenu until you navigate back to it; open User Note Categories and the Users submenu and the Notes / Note Categories sub-submenu are both still there.

Without the extension parameter

The screen remembers the last extension you looked at, per user, in your session. Reaching index.php?option=com_categories with no extension therefore usually shows the extension you were in last, and every link on the page carries it forward.

On a fresh session, with nothing remembered, the screen degrades in three ways at once. The permission check that guards it asks for core.manage on an empty extension name, which only a Super User passes, so everyone else gets a 404. Anyone who does get in finds the list applying no extension filter at all — every extension's categories, mixed together in one tree, with no column to tell them apart — and the - Select Max Levels - menu empty. Open a category from there and the edit form falls back to com_content, so saving would file it under Articles.

Always arrive through one of the menu entries above.

Nesting

Categories nest to any depth. The table stores the tree as a nested set: parent_id, lft and rgt bounds, a level number, and a path of slash-separated aliases.

All four extensions live in one tree. A hub installs a single root row — id 1, titled ROOT, alias root, level 0, extension system — and every category in every extension is a descendant of it. A top-level category is therefore level 1, and the list indents each row by level - 1.

Nothing enforces a maximum depth. level is an unsigned integer and no check anywhere counts it. The real limit is path, a varchar(255): the aliases of a category and all its ancestors are joined with / and stored there, and once that overflows 255 characters the path is silently truncated. For com_content the path is also the URL, so keep aliases short — see URLs.

The Parent menu on the form offers every category in the same extension plus - No parent -, and excludes the category being edited together with all of its descendants, so you cannot make a category its own child. To swap a parent and a child, move the child up rather than the parent down.

Saving any category rebuilds the tree from the root — every lft, rgt, level and path in the table, across all four extensions, is rewritten. This is normally invisible, but it is why a save on a large hub is not instant.

The category list

Above the list are a search box and four menus.

Filter	What it does
Filter:	Matches the text against the category title or description.
- Select Max Levels -	Shows only categories nested no deeper than the level you pick. The menu lists the depths that actually exist.
- Select Status -	Published, Unpublished, Archived, Trashed, or All.
- Select Access -	One access level.
- Select Language -	Nothing. See the warning below.

With no status filter set, the list shows everything except trashed categories. To see trashed categories, set - Select Status - to Trashed.

The columns are Title, Status, Ordering, Access, Language and ID. The alias sits under the title, with the category's note after it when it has one, and the full path is the title line's tooltip. Hovering the ID shows the row's lft and rgt bounds.

Sort by Ordering to enable the up and down arrows and the ordering boxes. Ordering is kept among siblings — the boxes number each category within its parent, not within the whole list — and the arrows only appear where there is a sibling to swap with on the page you are looking at.

Selecting one or more checkboxes enables the toolbar:

Button	What it does
New	Opens an empty category in the current extension.
Edit	Opens the selected category. Selecting the title does the same.
Publish / Unpublish	Sets the state to Published or Unpublished.
Archive	Sets the state to Archived.
Check In	Clears the checked-out flag on the selected categories.
Delete	Sets the state to Trashed. It does not delete anything.
Options	The owning component's configuration, not this one's.

The state buttons skip any category you lack core.edit.state on. They do say so, but the message is an untranslated developer string — Can't change state drop 0 — naming the row's position in the list rather than the category.

Batch processing

Batch is for the day a section is reorganised: twenty pages that need moving under a new parent, or a set of pages that should all become Registered at once. It is not a small convenience — moving a category moves its children with it, and a copy duplicates a whole branch, so check what you have ticked before you run it. There is no undo; reversing a batch means running another one back the other way.

Below the list, an administrator holding Create, Edit and Edit State on the extension gets a Batch process the selected categories panel. It sets the access level and the language of the checked categories, and moves or copies them — with all of their children — under another category. Copying leaves the originals alone and applies the other changes to the copies. A target category is mandatory: the batch is refused with No target category selected for batch processing without one, even if all you wanted to change was the access level.

The category form

New or Edit opens Category Manager: Add A New Articles Category or Category Manager: Edit Articles Category, with the extension's name in the middle. The toolbar is Save, Save & Close, Save as Copy, Save & New, Cancel and Help.

The main column holds:

Field	Notes
Title	Required.
Alias	The slug. Leave it blank and it is generated from the title: transliterated, lowercased, and reduced to letters, digits and hyphens. A title with nothing usable in it produces a timestamp instead.
Parent	- No parent - for a top-level category, or another category in the same extension.
Status	Published, Unpublished, Archived or Trashed.
Access	The viewing level. See Access levels.
Language	All, or one installed content language.
Description	Free text, in the site's default editor.

The right column shows the Extension, the ID, and who created and last modified the category and when, above two collapsible panels:

Panel	Holds
Basic Options	Alternative Layout, Image, and Note — a short private label shown after the alias in the list.
Metadata Options	Meta Description, Meta Keywords, Author and Robots.

The form is the same for every extension. Nothing lets a component add its own fields to a category, so a note category and an article category carry exactly the same information, including the layout and image options that only articles use.

An administrator also gets a Permissions block across the foot of the form, which sets this category's own rules and is inherited by its children and by the items filed in it.

The form also defines a read-only Path field that no template renders, so the stored path is only ever visible as the tooltip on the list's title.

States and permissions

A category has the same four states as an article — Published, Unpublished, Archived and Trashed — and they mean the same things. States, trash and check-in covers them.

What matters here is that a category's state and access level apply to everything inside it, not just to the category itself.

For articles this is enforced in the query. Every article listing walks the category path from the root down to the article's own category and checks each one:

• If any category on that path is not published, the article is treated as unpublished, whatever the article's own state says.
• If a category on that path is archived, the articles beneath it are treated as archived.
• The access filter is applied to the article's access level and to its category's, so an article in a Special category is not visible to a member who lacks Special, even if the article itself is Public.

So unpublishing a category is the way to take a whole branch off the site at once. Nothing is changed on the items themselves, and republishing the category brings them all back in the state they were already in.

The other three extensions do less. The knowledge base filters child categories by state and access when it lists them, and events lists only published categories; neither walks the whole path the way articles do. User note categories have no state or access behaviour at all — the note list's category filter is the only thing a note category changes, and the manager's Status and Access controls have no visible effect on notes.

Permissions on the Category Manager are checked against the owning extension, never against com_categories, which ships no access.xml of its own:

Check	Against	Controls
core.manage	The extension	Whether the screen opens at all. Without it you get a 404.
core.create	The extension, or a category	New, and which categories the Parent menu offers.
core.edit, core.edit.own	extension.category.id	Opening a category.
core.edit.state	extension.category.id	Publish, Unpublish, Archive, Delete, and whether you may move a category to a different parent.
core.delete	The extension	Showing the Delete button.
core.admin	The extension	The Permissions block and the Options button.

Because the asset name is built from the extension, the same administrator can be allowed to manage article categories and refused note categories. Set those permissions on the owning component's Options screen, or per category in the Permissions block; see Access groups.