Category Archives: Show posts categorized in parent category only

And this is the indirect way I am using now. If there is any better answer please do share.

while ( have_posts() ) {
    the_post();
    $cat = get_query_var('cat');
    $categories = wp_get_post_categories(get_the_ID());
    if (in_array($cat, $categories)) {
        ...
    }
} // end loop