How to automatically update ACF field value every year?

Question

I'm using ACF in my custom post type and I have 2 numeric fields: one for Birth year and another for Age. I want to update the age field automatically based on the birth year field value. I found out an acf filter that updates the field value before it is saved into the database and created the following function:

function update_acf_value_age( $value, $post_id, $field, $original ) {
    $birth_year = get_field( 'birth_year', $post_id );
    $value = date('Y') - $birth_year;

    return $value;
}
add_filter('acf/update_value/name=age', 'update_acf_value_age', 10, 4);

It is working fine and updates the age value every time I save a certain post. But I need it to be updated every year, ideally automatically. Is there a way to automatically force every post to be saved/updated yearly? Or is there a better approach to what I'm trying to accomplish?

I read about something called WP-Cron but I don't understand how to implement it and don't know if it's a good solution for this case.

Thanks in advance!

Answer 1

If you don't want to use a scheduler (ex: Action Scheduler) or a cron job, and you only want to update once per year, then an option that tracks the next update time is probably the simplest approach (untested):

add_action( 'init', static function () {
    $option_name = 'cpt_ages_next_update';
    $option      = absint( get_option( $option_name ) );

    if ( $option > time() ) {
        return;
    }

    $query = new WP_Query( array(
        'post_type'      => 'cpt',
        'posts_per_page' => -1,
        'fields'         => 'ids',
        'no_found_rows'  => true,
    ) );

    if ( ! $query->have_posts() ) {
        return;
    }

    foreach ( $query->posts as $post_id ) {
        $year = absint( get_field( 'birth_year', $post_id ) );
        $age  = absint( date( 'Y' ) ) - $year;

        update_field( 'age', $age );
    }

    update_option( $option_name, time() + YEAR_IN_SECONDS );
} );

I would recommend using a plugin like Action Scheduler though, especially if you the number of posts is very high.