php - codeigniter load model in core folder -

i'm new codeigniter , i'd load model in core/my_lang.php class.

class my_lang extends ci_lang {     /** array $languages array of languages */     var $languages = array('');      /** array $special special uris (not localized) **/     var $special = array('');      /** string $default_uri redirect if no language in uri */     var $default_uri = '';      public function getlanguages()     {         $this->load->model('lang_model');         return $this->lang_model->getlangs();     } 

of course example of i'm trying achieve. doesn't work , questions are:

• is practise this?
• if yes, how can load model in class?

i didn't load of core classes of ci .

the used class , load theme in autoload.php file instead of load them every time .