In this article by Joseph L. LeBlanc, you will learn about the architecture, design, and requirements of a general Joomla! component. You will also see how the component gets executed and is registered with the database. At the end, you will learn to create toolbars.

Joomla!'s Component Structure

Joomla! employs a specific naming scheme, which is used by all components. Each component in the system has a unique name with no spaces. The code is split into two folders, each bearing the component name prefixed by com_. The component used here will be called reviews. Therefore, you will have to create two folders named com_reviews:

• Create one in the folder named components for the front end.
• Create one in the folder named components within the administrator folder for the back end.

When the component is loaded from the front end, Joomla! will look for a file with the component's unique name ending in a .php extension. Within the components/com_reviews folder, create the reviews.php file. Similarly, running it in the back end assumes the presence of a file prefaced with admin. followed by the component name and ending in .php. Add the file admin.reviews.php in administrator/components/com_reviews. Leave both the files empty for the moment.

Executing the Component

All front-end requests in Joomla! go through index.php in the root directory. Different components can be loaded by setting the option variable in the URL GET string. If you install Joomla! on a local web server in a directory titled joomla, the URL for accessing the site will be http://localhost/joomla/index.php or something similar. Assuming this is the case, you can load the component's front end by opening http://localhost/joomla/index.php?option=com_reviews in your browser. At this point, the screen should be essentially blank, apart from the common template elements and modules. To make this component slightly more useful, open reviews.php and add the following code, then refresh the browser:

<?php
defined( '_JEXEC' ) or die( 'Restricted access' );
echo '<div class="componentheading">Restaurant Reviews</div>';
?>

Your screen will look similar to the following:

You may be wondering why we called defined() at the beginning of the file. This is a check to ensure that the code is called through Joomla! instead of being accessed directly at components/com_reviews/reviews.php. Joomla! automaticallyconfigures the environment with some security safeguards that can be defeated ifsomeone is able to directly execute the code for your component.

For the back end, drop this code into

administrator/components/com_reviews/admin.reviews.php:

<?php
defined( '_JEXEC' ) or die( 'Restricted access' );
echo 'Restaurant Reviews';
?>

Go to http://localhost/joomla/administrator/index.php?option=com_reviews and compare your result to this:

Joomla!'s Division between Front End and Back End

For all Joomla! components, code empowering the back-end portion is kept away from the front-end code. In some instances, such as the database table class, the back end will use certain files from the front end, but otherwise the two are separate. Security is enhanced as you are less likely to slip the administrative functions into the front-end code. This is an important distinction as the front end and back end are similar in structure.     

The following folder diagram shows the Joomla! root with the administrator folder expanded:

Notice that the administrator folder has a structure similar to the root folder. It is important to differentiate between the two, else you may place your code in the wrong folder and it will fail to execute until youmove it.