Developing a MVC Component/Using the database

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This tutorial is part of the Developing a Model-View-Controller (MVC) Component for Joomla!2.5 tutorial. You are encouraged to read the previous parts of the tutorial before reading this.

Using the database[edit]

Components usually manage their contents using the database. During the install/uninstall/update phase of a component, you can execute SQL queries through the use of SQL text files.

With your favorite file manager and editor create two files called admin/sql/install.mysql.utf8.sql and admin/sql/updates/mysql/0.0.6.sql. They should both have the same content, as follows:

admin/sql/install.mysql.utf8.sql and admin/sql/updates/mysql/0.0.6.sql

DROP TABLE IF EXISTS `#__helloworld`;

CREATE TABLE `#__helloworld` (
  `id` int(11) NOT NULL auto_increment,
  `greeting` varchar(25) NOT NULL,
   PRIMARY KEY  (`id`)

INSERT INTO `#__helloworld` (`greeting`) VALUES
	('Hello World!'),
	('Good bye World!');

The file install.mysql.utf8.sql will be executed when you install this component. The file 0.0.6.sql is executed when you do an update.

Important Note: When the component is installed, the files in the SQL updates folder (for example, admin/sql/updates/mysql) are read and the name of the last file alphabetically is used to populate the component's version number in the #__schemas table. This value must be in this table in order for the automatic update to execute the update SQL files for future versions. For this reason, it is good practice to create a SQL update file for each version (even if it is empty or just has a comment). This way the #__schemas version will always match the component version.

Important Note: When saving the SQL files in utf8, be sure to save them as utf8 NO BOM or the query will fail with MySQL error #1064.

This is the install file. It will be executed if you put an appropriate order in the helloworld.xml file


<?xml version="1.0" encoding="utf-8"?>
<extension type="component" version="2.5.0" method="upgrade">

	<name>Hello World!</name>
	<!-- The following elements are optional and free of formatting constraints -->
	<creationDate>November 2009</creationDate>
	<author>John Doe</author>
	<copyright>Copyright Info</copyright>
	<license>License Info</license>
	<!--  The version string is recorded in the components table -->
	<!-- The description is optional and defaults to the name -->
	<description>Description of the Hello World component ...</description>

	<install> <!-- Runs on install -->
			<file driver="mysql" charset="utf8">sql/install.mysql.utf8.sql</file>
	<uninstall> <!-- Runs on uninstall -->
			<file driver="mysql" charset="utf8">sql/uninstall.mysql.utf8.sql</file>
	<update> <!-- Runs on update; New in 2.5 -->
			<schemapath type="mysql">sql/updates/mysql</schemapath>

	<!-- Site Main File Copy Section -->
	<!-- Note the folder attribute: This attribute describes the folder
		to copy FROM in the package to install therefore files copied
		in this section are copied from /site/ in the package -->
	<files folder="site">

		<!-- Administration Menu Section -->
		<menu>Hello World!</menu>
		<!-- Administration Main File Copy Section -->
		<!-- Note the folder attribute: This attribute describes the folder
			to copy FROM in the package to install therefore files copied
			in this section are copied from /admin/ in the package -->
		<files folder="admin">
			<!-- Admin Main File Copy Section -->
			<!-- SQL files section -->
			<!-- tables files section -->
			<!-- models files section -->


Do the same for the uninstall file:

With your favorite file manager and editor put a file admin/sql/uninstall.mysql.utf8.sql containing:


DROP TABLE IF EXISTS `#__helloworld`;

Adding a new field type[edit]

For the moment, we have used a hard coded field type for messages. We need to use our database for choosing the message.

Modify the site/views/helloworld/tmpl/default.xml file and put these lines


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

It introduces a new field type and tells Joomla to look for the field definition in the /administrator/components/com_helloworld/models/fields folder.

With your favorite file manager and editor put a file admin/models/fields/helloworld.php file containing:


// No direct access to this file
defined('_JEXEC') or die;

// import the list field type

 * HelloWorld Form Field class for the HelloWorld component
class JFormFieldHelloWorld extends JFormFieldList
	 * The field type.
	 * @var		string
	protected $type = 'HelloWorld';

	 * Method to get a list of options for a list input.
	 * @return	array		An array of JHtml options.
	protected function getOptions() 
		$db = JFactory::getDBO();
		$query = $db->getQuery(true);
		$messages = $db->loadObjectList();
		$options = array();
		if ($messages)
			foreach($messages as $message) 
				$options[] = JHtml::_('select.option', $message->id, $message->greeting);
		$options = array_merge(parent::getOptions(), $options);
		return $options;

The new field type displays a drop-down list of messages to choose from. You can see the result of this change in the menu manager section for the helloworld item.

Display the chosen message[edit]

When a menu item of this component is created/updated, Joomla stores the identifier of the message. The HelloWorldModelHelloWorld model has now to compute the message according to this identifier and the data stored in the database.

Modify the site/models/helloworld.php file:


// No direct access to this file
defined('_JEXEC') or die('Restricted access');

// import Joomla modelitem library

 * HelloWorld Model
class HelloWorldModelHelloWorld extends JModelItem
	 * @var array messages
	protected $messages;

	 * Returns a reference to the a Table object, always creating it.
	 * @param	type	The table type to instantiate
	 * @param	string	A prefix for the table class name. Optional.
	 * @param	array	Configuration array for model. Optional.
	 * @return	JTable	A database object
	 * @since	2.5
	public function getTable($type = 'HelloWorld', $prefix = 'HelloWorldTable', $config = array()) 
		return JTable::getInstance($type, $prefix, $config);
	 * Get the message
	 * @param  int    The corresponding id of the message to be retrieved
	 * @return string The message to be displayed to the user
	public function getMsg($id = 1) 
		if (!is_array($this->messages))
			$this->messages = array();
		if (!isset($this->messages[$id])) 
                        //request the selected id
			$jinput = JFactory::getApplication()->input;
			$id = $jinput->get('id', 1, 'INT' );

			// Get a TableHelloWorld instance
			$table = $this->getTable();

			// Load the message

			// Assign the message
			$this->messages[$id] = $table->greeting;
		return $this->messages[$id];

The model now asks the TableHelloWorld to get the message. This table class has to be defined in admin/tables/helloworld.php file


// No direct access
defined('_JEXEC') or die('Restricted access');

// import Joomla table library

 * Hello Table class
class HelloWorldTableHelloWorld extends JTable
	 * Constructor
	 * @param object Database connector object
	function __construct(&$db) 
		parent::__construct('#__helloworld', 'id', $db);

You shouldn't see any differences, but if you access the database you should see a table named jos_helloworld with two columns: id and greeting. And two entries: Hello World! and Good bye World

Packaging the component[edit]

Content of your code directory

Create a compressed file of this directory or directly download the archive and install it using the extension manager of Joomla. You can add a menu item of this component using the menu manager in the backend.

Note: site/models/helloworld.php is not up-to-date as mentioned on this page. You need to copy the code yourself.


Prev: Adding a variable request in the menu type Next: Basic backend


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