update_post_meta not working in function

Question

I am attempting to take some custom field meta data (generated via the ACF plugin) and save it as post meta with a function. This is what I've come up with:

function tps_create_slotcode($post_id) {
    if (get_post_type($post_id) == 'space-rental') {
        $slotCodes = array();
        while (have_rows('dates_and_times', $post_id)) {
            the_row();
            $date = get_sub_field('date');
                $dateStamp = strtotime($date);
            $start = get_sub_field('start_time');
            $end = get_sub_field('end_time');
            $space = get_sub_field('space'); //term id
                $spaceTerm = get_term($space, 'spaces');

            $slotCodes[] = $spaceTerm->slug.'_'.$start.'_'.$date;
        }
        update_post_meta($post_id, 'slotCodes', $slotCodes);
    }
}
add_action('acf/save_post', 'tps_create_slotcode', 40);

I have tested all variable to make sure they are producting a value, and they are, but the update_post_meta call is not doing anything.

If I put the update_post_meta INSIDE the loop, it works but only saves the last result (obviously) since that's the last iteration of the loop. That would be this code:

    function tps_create_slotcode($post_id) {
        if (get_post_type($post_id) == 'space-rental') {
            while (have_rows('dates_and_times', $post_id)) {
                the_row();
                $date = get_sub_field('date');
                    $dateStamp = strtotime($date);
                $start = get_sub_field('start_time');
                $end = get_sub_field('end_time');
                $space = get_sub_field('space'); //term id
                    $spaceTerm = get_term($space, 'spaces');

                $slotCodes = $spaceTerm->slug.'_'.$start.'_'.$date;
update_post_meta($post_id, 'slotCodes', $slotCodes);
            }
            update_post_meta($post_id, 'slotCodes', $slotCodes);
        }
    }
    add_action('acf/save_post', 'tps_create_slotcode', 40);

Can anyone tell me what I'm doing wrong in the first example? Will update_post_meta not save an array of data or something?

Answer 1

Figured it out. I had to re-read the codex a lot to figure out that when you pass an array to update_post_meta it is serialized. By using maybe_unserialize() on the return value I was able to to get access to the values. Hope this helps some future searcher!