How can I set and update the the_date according to a custom field of the post

Question

How can I set and update the the_date according to a custom field of the post?

I have a custom field "date-time" with the following format yyyy-mm-dd hh:mm

e.g. 2015-09-30 08:12

I'd like this date to over-ride the normal date and time of the post, both on publish and when updated.

Answer 1

Normally you would write a function that gets called by the save_post hook, and use wp_update_post to update the post. The problem is, when you call wp_update_post it calls save_post, which will cause an infinite loop.

To get around that, we will unhook our function before calling wp_update_post, then re-hook it afterward.

I have not tried this, but it should work:

function change_post_date( $post_id, $post ) {

    // WordPress calls "save_post" when a post is saved, updated, autosaved,
    // revision created, or ajax called. We only want to execute this function
    // during post save and update. The next 3 "if" statements check to see why
    // save_post was called...

    // Autosave? Do nothing
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
        return;
    // AJAX? Do nothing
    if ( defined( 'DOING_AJAX' ) && DOING_AJAX )
        return;
    // Post revision? Do nothing
    if ( false !== wp_is_post_revision( $post_id ) )
        return;

    // Make sure the person editing the post has permission to do so
    if ( ! current_user_can( 'edit_post', $post_id ) )
        return;

    // Get the "date-time" field
    $date_time_field = get_post_meta($post_id, 'date-time', true);

    // Unhook
    remove_action('save_post', 'change_post_date', 10);

    $args = array (
        'ID' => $post_id,
        'post_date' => $date_time_field,
        'post_date_gmt' => gmdate('Y-m-d H:i', $date_time_field )
    );

    wp_update_post( $args );

    // Re-hook
    add_action('save_post', 'change_post_date', 10);

}
add_filter('save_post', 'change_post_date', 10, 2);