MVC Anatomy: Site Files

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File Structure[edit]

There are fewer files in the Site part of the component than in the Administrator part so this seems like a good place to start. Only those parts of each file that need explanation will be covered. It is best if you open each file being mentioned, have a look at the overall content and then find the parts being explained. The alphabet order of the file structure is as follows:

 |- forms
    |- filter_countries.xml
 |- language
    |- en-GB
       |- com_countrybase.ini
 |- src
    |- Controller
       |- DisplayController
    |- Model
       |- CountriesModel.php
    |- Service
       |- Router.php
    |- View
       |- Countries
          |- HtmlView.php
 |- tmpl
    |- countries
       |- default.php
       |- default.xml


The complete file in a scrollable div:

 * @package     Countrybase.Site
 * @subpackage  com_countrybase
 * @copyright   (C) 2022 Clifford E Ford
 * @license     GNU General Public License version 2 or later; see LICENSE.txt

namespace J4xdemos\Component\Countrybase\Site\Controller;

defined('_JEXEC') or die;

use Joomla\CMS\MVC\Controller\BaseController;
use Joomla\CMS\Router\Route;
use Joomla\CMS\Session\Session;

 * Countrybase Component Controller
 * @since  4.0.0
class DisplayController extends BaseController
	 * The default view.
	 * @var    string
	 * @since  1.6
	protected $default_view = 'countries';

	protected $app;

Parts of this file are explained as follows:

Copyright Notice[edit]

Every php file should start with a copyright notice like the following:

 * @package     Countrybase.Site
 * @subpackage  com_countrybase
 * @copyright   (C) 2022 Clifford E Ford
 * @license     GNU General Public License version 2 or later; see LICENSE.txt

If you frequently create new files and copy/paste this section remember to update the component name and copyright notice.

Namespace and defined check[edit]

Following the copyright notice every php file must have a line containing defined('_JEXEC') or die; except that namespaced files must declare the namespace before any other php code, so before the defined check. Namespaced php files are those containing component php classes in the src folder or its sub-folders.

namespace J4xdemos\Component\Countrybase\Site\Controller;

defined('_JEXEC') or die;

The defined check prevents a php file from being executed by calling it directly via its url. The _JEXEC constant is defined when the application starts via the root or administrator index.php file. It is an important security aid.

Combined with the namespace declared in in the countrybase.xml manifest file, Joomla will look for any class declared in the current file in root/components/com_countrybase/src/Controller - in this case appending the name of this file, DisplayController.php

use Statements[edit]

The use statements usually follow the defined check and are often listed in alphabet order. The use statements define the locations of the classes used by this php file. Sometimes, use statements are there by mistake, being declared but not used. That does no harm but ought to be corrected. There are two unused statements here:

use Joomla\CMS\MVC\Controller\BaseController;
use Joomla\CMS\Router\Route;
use Joomla\CMS\Session\Session;

Controller Class[edit]

The display controller has almost nothing to do as all the work is done in the parent class. The one important thing it does is set the default view, in this case countries. That will cause the default component view to use the Countries/HtmlView.php and tmpl/countries/default.php files to display the countries data.

 * Countrybase Component Controller
 * @since  4.0.0
class DisplayController extends BaseController
	 * The default view.
	 * @var    string
	 * @since  1.6
	protected $default_view = 'countries';

	protected $app;

The code layout is a Joomla standard layout for php (https://developer.joomla.org/coding-standards/basic-guidelines.html). The documentation blocks are designed for automated documentation of code. The since values illustrated here are for Joomla 4 code.

Do not forget to set the $default_view for this controller. Without it, the DisplayController will use the the default view defined in the component configuration file or, if that does not exist, the component name.


The controller has set the default view to countries so the next step is to load the corresponding HtmlView.php code. Parts of this file requiring some explanation.

Class variables[edit]

class HtmlView extends BaseHtmlView
	 * The model state
	 * @var  \Joomla\CMS\Object\CMSObject
	protected $state = null;
	protected $items = null;
	protected $pagination = null;
	public $filterForm;
	public $activeFilters;

The class variables are used to store information about the page to be displayed:

  • $state - the model state, often primed by form or query string input.
  • $items - the list of country data retrieved from the database.
  • $pagination - an object used to display a page navigation mechanism if there are more pages than the list limit, normally 20 items.
  • $filterForm - not usually found in site pages but used in com_countrybase to filter by country name or published state.
  • $activeFilters - used to keep track of which filters are in use.

display function[edit]

This is fairly standard for a site view, apart from the filterForm and activeFilters parts:

	public function display($tpl = null)
		$this->state      = $this->get('State');
		$this->items      = $this->get('Items');
		$this->pagination = $this->get('Pagination');
		$this->filterForm    = $this->get('FilterForm');
		$this->activeFilters = $this->get('ActiveFilters');

		// Flag indicates to not add limitstart=0 to URL
		$this->pagination->hideEmptyLimitstart = true;

		// Check for errors.
		if (count($errors = $this->get('Errors')))
			throw new GenericDataException(implode("\n", $errors), 500);


The statements of the form $this->get('Xxxx') cause Joomla to look in CountriesModel.php for a function named getXxxx() and return any data executed by that code for storage and use in the view. Often the function is in the CountriesModel parent. For example the getItems function is not present in CountriesModel.php but is present in the ListModel that it extends.

In summary the view class retrieves data from the model and then calls its parent class to display the data.


There are a small number of functions in the Model that you usually need to complete yourself. Others are inherited from the parent ListModel.


It is normal practice to include in the constructor any filter fields that you may wish to use. Without them, filters may appear to have no effect. They are often forgotten when you wish to add a filter some time later. Each field is given as its field name and with a table name alias, usually a, b, c and so on, but can be anything you choose that is consistent with code elsewhere.

	public function __construct($config = array())
		if (empty($config['filter_fields']))
			$config['filter_fields'] = array(
					'id', 'a.id',
					'title', 'a.title',
					'iso_2', 'a.iso_2',
					'iso_3', 'a.iso_3',
					'country_code', 'a.country_code',
					'region_code', 'a.region_code',
					'state', 'a.state',
					'subregion_code', 'a.subregion_code',
					'phone_prefix', 'a.phone_prefix',
					'currency_code', 'a.currency_code',



This functions takes input parameters and prepares them for use in a database query. Some parameters are handled in the parent so there is no need to do anything here. For example, if the search field is title that is handled by the parent, as are the state and pagination start and limit fields.

	protected function populateState($ordering = 'title', $direction = 'ASC')
		// List state information.
		parent::populateState($ordering, $direction);


This function creates a hash to store a query for use elsewhere.

	protected function getStoreId($id = '')
		// Compile the store id.
		$id .= ':' . $this->getState('filter.search');
		$id .= ':' . $this->getState('filter.published');

		return parent::getStoreId($id);


This is where the query is created to extract data from the database. it requires some understanding of how queries are constructed.

	protected function getListQuery()
		// Create a new query object.
		$db    = $this->getDbo();
		$query = $db->getQuery(true);

		// Select the required fields from the table.
					$db->quoteName('b.title') . ' AS currency_title',
		->from($db->quoteName('#__countrybase_countries', 'a'))
		->leftjoin($db->quoteName('#__countrybase_currencies', 'b') . 'ON a.currency_code = b.currency_code');

		// Filter by search in title.
		$search = $this->getState('filter.search');

		if (!empty($search))
			$search = $db->quote('%' . str_replace(' ', '%', $db->escape(trim($search), true) . '%'));
			$query->where('(a.title LIKE ' . $search . ')');

		// Filter by published state
		$published = (string) $this->getState('filter.published');

		if ($published !== '*')
			if (is_numeric($published))
				$state = (int) $published;
				$query->where($db->quoteName('a.state') . ' = :state')
				->bind(':state', $state, ParameterType::INTEGER);

		// Add the list ordering clause.
		$orderCol  = $this->state->get('list.ordering', 'a.title');
		$orderDirn = $this->state->get('list.direction', 'ASC');

		$query->order($db->escape($orderCol) . ' ' . $db->escape($orderDirn));
		return $query;


  • getQuery(true) gets a new empty query object.
  • $query->select() adds a SELECT statement. There can be multiple select statements - Joomla concatenates them.
  • table aliases a and b notice that some columns come from different tables.
  • ->from() defines which table is table a. this can be in a separate statement: $query->from();
  • ->leftjoin() defines table b and how it is to be joined to table a.
  • $query->where() makes use of any filters defined, one for search and another for state.
  • return $query there is no parent call, everything in the query must be set up here.


This is the part of the code where the html content is created. At the very least it may just contain <h1>Hello World</h1>. For the list of countries a table is needed with a heading row and one row for data on each country. As there are 250 countries a pagination mechanism is needed to display a subset of countries a few at a time. That requires a form. And in this case a standard Joomla searchtools bar is useful. This is it:

 * @package     Countrybase.Site
 * @subpackage  com_countrybase
 * @copyright   (C) 2022 Clifford E Ford
 * @license     GNU General Public License version 2 or later; see LICENSE.txt

\defined('_JEXEC') or die;

use Joomla\CMS\HTML\HTMLHelper;
use Joomla\CMS\Language\Text;
use Joomla\CMS\Layout\LayoutHelper;
use Joomla\CMS\Router\Route;

$listOrder = $this->escape($this->state->get('list.ordering'));
$listDirn  = $this->escape($this->state->get('list.direction'));

<h1><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES'); ?></h1>

<form action="<?php echo Route::_('index.php?option=com_countrybase'); ?>" method="post" name="adminForm" id="adminForm">

<?php echo LayoutHelper::render('joomla.searchtools.default', array('view' => $this)); ?>

<div class="table-responsive">
	<table class="table table-striped">
	<caption><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_TABLE_CAPTION'); ?></caption>
		<th scope="col">
			<?php echo HTMLHelper::_('searchtools.sort', 'COM_COUNTRYBASE_COUNTRIES_COUNTRY', 'a.title', $listDirn, $listOrder); ?>
		<th scope="col"><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_ISO_2'); ?></th>
		<th scope="col"><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_ISO_3'); ?></th>
		<th scope="col"><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_CURRENCY_TITLE'); ?></th>
		<th scope="col"><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_CURRENCY_SYMBOL'); ?></th>
		<th scope="col"><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_CURRENCY_CODE'); ?></th>
		<th scope="col"><?php echo Text::_('COM_COUNTRYBASE_COUNTRIES_XRATE'); ?></th>
	<?php foreach ($this->items as $id => $item) : ?>
		<td><?php echo $item->title; ?></td>
		<td><?php echo $item->iso_2; ?></td>
		<td><?php echo $item->iso_3; ?></td>
		<td><?php echo $item->currency_title; ?></td>
		<td><?php echo $item->symbol; ?></td>
		<td><?php echo $item->currency_code; ?></td>
		<td><?php echo $item->dollar_exchange_rate; ?></td>
	<?php endforeach; ?>

<?php echo $this->pagination->getListFooter(); ?>

<input type="hidden" name="task" value="">
<input type="hidden" name="boxchecked" value="0">
<?php echo HTMLHelper::_('form.token'); ?>


Points to note:

  • $listOrder and $listDirection are used to order by column heading. Only the title has been set up to do that.
  • form action is typically set up to refer to itself.
  • LayoutHelper::render('joomla.searchtools.default',...) creates a search bar of the type seen in administrator list pages. It needs a filter form!
  • $this->pagination->getListFooter() fetches the html code for the pagination widget.
  • task this hidden field is filled out by javascript when the form is submitted.
  • boxchecked this hidden field is used when one or more row checkboxes are selected for batch operation. Not really needed here!
  • HTMLHelper::_('form.token'); gets the code for a form token used as a security device for form submissions involving data submission. Not really needed here!


This file is used to create a menu item. It has the same name as the php file, so default.xml in this case.

<?xml version="1.0" encoding="UTF-8"?>

	<!-- Add fields to the parameters object for the layout. -->
	<fields name="params">

		<!-- Options -->
		<fieldset name="options">



  • help url points to a help file in the administrator folder. It allows you to create your own local help files, invoked from the menu edit form Help button after selecting the Countrybase Default View menu type.
  • params allows you to use parameters, for example whether or not to show a particular column in the countries list. No parameters have been specified yet.
  • key translations need to be in the administrator/language/en-GB/countrybase.sys.ini file.


This file is needed for the search bar. Without it, Joomla will throw a fatal error. The file name must be exactly as shown: the view name preceded by filter_. The content is simple, just definitions for the search field and any other filters you may wish to use.

<?xml version="1.0" encoding="utf-8"?>

	<fields name="filter">


			<option value="">JOPTION_SELECT_PUBLISHED</option>


Note that any string keys starting with J are Joomla defined and you should not include them in your language files.


Joomla always loads English language keys before any other language. This ensures that keys do not appear in the output if a language is incompletely translated. Because the language keys are long words in pseudo-English it is considered better to have a mixture of English and another language than a mixture of keys and another language. If another language is in use Joomla overwrites the English strings with those of the other language.

Note that it is common practice to list the strings in key alphabet order:

; Joomla! Project
; (C) 2005 Open Source Matters, Inc. <https://www.joomla.org>
; License GNU General Public License version 2 or later; see LICENSE.txt
; Note : All ini files need to be saved as UTF-8



The Router is required for SEO urls. Without it a menu link may appear as option=com_countrybase&view=countries. With it a link will appear as country-base.html or whatever name you choose for the link title alias.

	public function __construct(SiteApplication $app, AbstractMenu $menu,
			CategoryFactoryInterface $categoryFactory, DatabaseInterface $db)

		$countries = new RouterViewConfiguration('countries');

		parent::__construct($app, $menu);

		$this->attachRule(new MenuRules($this));
		$this->attachRule(new StandardRules($this));
		$this->attachRule(new NomenuRules($this));

If there are more views, for example a table of currencies, you would define each view here before the parent::__construct() statement.

Related Tutorials[edit]

MVC Anatomy[edit]