Why we use getState() in select statement of query while retriving data in Joomla?

Question

I'm learning Joomla Extension development and overriding getListQuery() method of a model that extends JModelList.

Now the problem is that we can retrieve a list of data from database using following which is working fine:

$db = $this->getDbo();
$query = $db->getQuery(true);
$query->select('id,title,state,company')->from($db->quoteName('#__books'));

But my ebook use following statement

$query->select(
$this->getState('list.select','a.id, a.title,' .'a.state, a.company'));

I understand the getState() method but why does the ebook author use getState() in select statement? What is the purpose of using this and where the 'list.select' property will be defined?

Answer 1

Using state in the select statement allows external extensions to use your method individually and to get different sets of data from it.

A good example is mod_articles_news module helper which sets the fields for selection from the Articles Model:

// Get an instance of the generic articles model
$model = JModelLegacy::getInstance('Articles', 'ContentModel', array('ignore_request' => true));

... 

$model->setState('list.select', 'a.fulltext, a.id, a.title, a.alias, a.introtext, a.state, a.catid, a.created, a.created_by, a.created_by_alias,' .
' a.modified, a.modified_by, a.publish_up, a.publish_down, a.images, a.urls, a.attribs, a.metadata, a.metakey, a.metadesc, a.access,' .
' a.hits, a.featured, a.language');

...

$items = $model->getItems();