Migrating custom module to Joomla 4

Question

I have a Joomla 3.x module which calls the category name from the database and then shows this in the module position.

It does this with:

    $db = &JFactory::getDBO(); 
    $id = JRequest::getString('id'); 
    $view = JRequest::getString('view'); 

    if ($view == 'category') {
        $sql = "SELECT title FROM #__categories WHERE #__categories.id = $id";
    } else {
        $sql = "SELECT #__categories.title FROM #__content, #__categories WHERE #__content.catid = #__categories.id AND #__content.id = $id";
    }

    $db->setQuery($sql); 
    $category = $db->loadResult(); 
    echo '<h1>' . $category . '</h1>'; 

This works in Joomla 3, but in Joomla 4 I'm getting an error:

Attempted to load class "JRequest" from the global namespace.

What's the best way to get this working in Joomla 4?

Answer 1

JRequest was deprecated in Joomla 2.5 (I think), so you can now use JInput, like so:

use Joomla\CMS\Factory;

$db = Factory::getDbo();
$input = Factory::getApplication()->input;
$id = $input->get('id');
$view = input->get('view');

You'll definitely want to update your database query, using more modern methods: https://docs.joomla.org/Selecting_data_using_JDatabase

If I'm not mistaken, you're currently prone to SQL injections.

Answer 2

Lodder's answer is fully valid, however he did not want to waste time to reformulate the query part of this old script in the question. As a morning drill during my coffee time I corrected that part too:

use Joomla\CMS\Factory; 

// get the Input object if $this->input is not avail
$app = Factory::getApplication();
$input = $app->input; 

// $db = Factory::getDbo();
$db = Factory::getContainer()->get('DatabaseDriver');

$id = $input->get('id', '', 'string');
$view = $input->get('view', '', 'string');    
    
$query = $db->getQuery(true);

if ($view == 'category') {

    $query->select('title')
        ->from($db->quoteName('#__categories'))
        ->where($db->quoteName('id') . ' = :id')
        ->bind(':id', $id);

} else {
    
    $query->select('b.title')
        ->from($db->quoteName('#__content', 'a'))
        ->innerJoin($db->quoteName('#__categories', 'b') . ' ON a.catid = b.id')
        ->where($db->quoteName('a.id') . ' = :id')
        ->bind(':id', $id);
}

$db->setQuery($query);
$category = $db->loadResult(); 
echo '<h1>' . $category . '</h1>';

Answer 3

$input = $app->input; is deprecated too. You should use in Joomla 4 $input = $app->getInput(); instead.

Also you can load database form DI container by this code:

use Joomla\Database\DatabaseInterface;
$db = Factory::getContainer()->get(DatabaseInterface::class);