Calculate and save an average in a meta

Question

I'm asking for your help to develop a system average. I have a website video games and I created a function that automatically calculates the average for each review. It works very well. The problem is that I would like to display in my sidebar Rated 5 games. Unfortunately, I can not ask WP to calculate and compare each mean. It will take a lot of time. So I'd like to do is calculated at the publication of the review in the admin to save automatically mean a meta. I do not know anything about the possibility in the administration. Is it possible? If yes, how? thank you

/* RATE */

function get_rate_overall($rate=bool){

    $graphics = get_field('graphics');
    $gameplay = get_field('game-play');
    $life = get_field('life');
    $sound = get_field('sound');

    $overall = $graphics + $gameplay + $life + $sound;
    $overall = $overall / 4;
    if (is_float($overall)) { $overall = number_format($overall,1); }
    if ($rate == true) { echo $overall.'/10'; }
    if ($rate == false) { echo $overall; }  
}

Answer 1

You can accomplish this via the save_post action:

add_action( 'save_post', 'wpa78558_save_average_meta', 100 );

function wpa78558_save_average_meta( $post_id ) {

    if ( !wp_is_post_revision( $post_id ) ) {

        $graphics = get_field('graphics', $post_id);
        $gameplay = get_field('game-play', $post_id);
        $life = get_field('life', $post_id);
        $sound = get_field('sound', $post_id);

        $overall = $graphics + $gameplay + $life + $sound;
        $overall = $overall / 4;
        if (is_float($overall)) { $overall = number_format($overall,1); }

        update_post_meta($post_id, 'overall', $overall);

    }

}

You can add additional checks in here for a specific post type (see example on save_post codex page), or verify that your field values exist before saving the meta data.

The average will be saved under the meta key overall and can be output in the template or referenced in a query.