Getting latest article from category including subcategories

Question

I am attempting to get the latest article in a category that has a number of subcategories through the Articles ContentModel.

If I use $model->setState('filter.category_id', $this->category->id);, it does not return anything due to the category in question not containing any articles; all of the articles are in subcategories.

How do I get all articles in the current category including children?

Code in question:

$model = JModelLegacy::getInstance('Articles', 'ContentModel', array('ignore_request' => true));
$model->getState();

// Set application parameters in model
$app = JFactory::getApplication();
$appParams = $app->getParams();
$model->setState('params', $appParams);

// Set the filters based on the module params
$model->setState('list.start', 0);
$model->setState('list.limit', 1);
$model->setState('filter.category_id', $this->category->id);
$model->setState('filter.published', 1);

// Permissions
$access = !JComponentHelper::getParams('com_content')->get('show_noauth');
$authorised = JAccess::getAuthorisedViewLevels(JFactory::getUser()->get('id'));
$model->setState('filter.access', $access);

// Featured Item

// Get article from featured set
// $model->setState('filter.featured', 'only');

// Ordering
$model->setState('list.ordering', 'a.publish_up');
$model->setState('list.direction', 'DESC');

$items = $model->getItems();

Answer 1

You need to enable subcategories with the subcategories.filter and also specify the levels of subcategories you want to go deep down.

$model->setState('filter.subcategories', true);
$model->setState('filter.max_category_levels', $subCategoryLevels);

Note that the subcategories check will occur, if the category id for the filter.category_id is numeric, otherwise if you pass an array of category ids (e.g. coming from a multiple choice select field), then the model will not look for subcategories, but it will load the articles for the given categories ids.