Developing a MVC Component/Using the database

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< J2.5:Developing a MVC Component
Revision as of 16:39, 29 November 2010 by Cdemko (Talk | contribs)


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This tutorial is part of the Developing a Model-View-Controller (MVC) Component for Joomla!1.6 tutorial. You are encouraged to read the previous parts of the tutorial before reading this.

Using the database

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 put two files admin/sql/install.mysql.utf8.sql and admin/sql/updates/mysql/0.0.6.sql containing:

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

DROP TABLE IF EXISTS `#__helloworld`;
CREATE TABLE `#__helloworld` (
  `greeting` varchar(25) NOT NULL,
   PRIMARY KEY  (`id`)
INSERT INTO `#__helloworld` (`greeting`) VALUES
	('Hello World!'),
	('Good bye World!');

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


<?xml version="1.0" encoding="utf-8"?>
<extension type="component" version="1.6.0" method="upgrade">
	<name>Hello World!</name>
	<!-- The following elements are optional and free of formatting conttraints -->
	<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 1.6 -->
			<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

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"?>
	<fields name="request">
		<fieldset name="request">
				<option value="1">Hello World!</option>
				<option value="2">Good bye World!</option>

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

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 string msg
	protected $msg;
	 * Returns a reference to the a Table object, always creating it.
	 * @param	type	The table type to instantiate
	 * @param	string	A prefix for the table class name. Optional.
	 * @param	array	Configuration array for model. Optional.
	 * @return	JTable	A database object
	 * @since	1.6
	public function getTable($type = 'HelloWorld', $prefix = 'HelloWorldTable', $config = array()) 
		return JTable::getInstance($type, $prefix, $config);
	 * Get the message
	 * @return string The message to be displayed to the user
	public function getMsg() 
		if (!isset($this->msg)) 
			$id = JRequest::getInt('id');
			// Get a TableHelloWorld instance
			$table = $this->getTable();
			// Load the message
			// Assign the message
			$this->msg = $table->greeting;
		return $this->msg;

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

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!1.6. You can add a menu item of this component using the menu manager in the backend.


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


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