coddeigniter cache library

[eluser]nani[/eluser]
Thanks
where to use the cache call
before calling the model function or
after the model call or
i have to check for cache and if its not exist then i have call model function and then cache..

i have this doubts...please help me i'm first time implementing cache...

Code:

// cache modal call
$courses_list = $this->cache->model('get_course_data', 'simpleSearch', array($search_params), 120);
// call to the model function
$courses_list = $this->get_course_data->simpleSearch($search_params);

am i going wrong.....