Using wp_ajax and wp_ajax_nopriv hooks

I want to send an ajax request and want to process it if the user is logged in. Therefore I want to use following two hooks, but I am not sure if I am using them correctly.

Is it correct to use same function take_action_function for the both hooks, and then check in the function if the user is logged in or not? Or should I create two different functions, one for the take action and other one just to return the message that user should be logged in?

add_action('wp_ajax_nopriv_test-action', 'take_action_function');
add_action('wp_ajax_test-action', 'take_action_function');

function take_action_function(){
    if ( is_user_logged_in() ){
       echo "success";
       die;
    } else {
        echo "not logged";
        die;
    }
}

It depends on what exactly you want to do. If you want to show just a short message, use the same callback for both.

But if you need completely different objects and load different additional files depending on the log-in status, use separate callbacks.

Basic example, probably not a recommended implementation. 🙂

class Ajax_Controller {

    public function __construct( $action ) {

        add_action( "wp_ajax_nopriv_$action", array ( $this, 'logged_out' ) );
        add_action( "wp_ajax_$action",        array ( $this, 'logged_in' ) );
    }

    public function logged_out() {

        require_once __DIR__ . '/Logged_Out_Data_Interface.php';
        require_once __DIR__ . '/Logged_Out_Data.php';
        require_once __DIR__ . '/Logged_Out_View.php';

        $data = new Logged_Out_Data;
        $view = new Logged_Out_View( $data );
        $view->render();
    }

    public function logged_in() {

        require_once __DIR__ . '/Logged_In_Data_Interface.php';
        require_once __DIR__ . '/Logged_In_Data.php';
        require_once __DIR__ . '/Logged_In_View.php';

        $data = new Logged_In_Data;
        $view = new Logged_In_View( $data );
        $view->render();
    }
}

Look at your use case, be pragmatic. When in doubt, compare the performance and the complexity of both approaches.