Automatically set page order on create page

Question

Is there a way to automatically set page order to the last order number upon creating new pages instead of having it set to 0?

Answer 1

You could use ajax and the admin_footer-post-new.php hook. The sql would vary depending on whether you want the highest or most recently published order number. The following returns the highest published order number + 1:

function wpse155926_set_menu_order() {
    $ret = array();

    if ( check_ajax_referer( 'wpse155926_set_menu_order_post', 'nonce', false /*die*/ ) ) {
        global $wpdb;
        //last published
        //$sql = $wpdb->prepare( 'SELECT menu_order FROM ' . $wpdb->posts . ' WHERE post_type = %s AND post_status = %s ORDER BY post_date DESC LIMIT 1', 'page', 'publish' );
        //highest published
        $sql = $wpdb->prepare( 'SELECT menu_order FROM ' . $wpdb->posts . ' WHERE post_type = %s AND post_status = %s ORDER BY menu_order DESC LIMIT 1', 'page', 'publish' );
        if ( ( $result = $wpdb->get_var( $sql ) ) !== false ) {
            $ret['menu_order'] = $result + 1;
        }
    }

    header('Content-type: application/json');
    die( json_encode( $ret ) );
}
add_action( 'wp_ajax_wpse155926_set_menu_order', 'wpse155926_set_menu_order' );

function wpse155926_admin_footer_post_new_php() {
?>
<script type="text/javascript">
jQuery(document).ready(function() {
    (function ($) {
        $.post( ajaxurl, {
                action: 'wpse155926_set_menu_order',
                nonce: <?php echo json_encode( wp_create_nonce( 'wpse155926_set_menu_order_post' ) ); ?>
            }, function(response) {
                if (response && response.menu_order) {
                    $('#pageparentdiv input[name="menu_order"]').val(response.menu_order);
                }
            }, 'json'
        );
    })(jQuery);
});
</script>
<?php
}
add_action( 'admin_footer-post-new.php', 'wpse155926_admin_footer_post_new_php' );

Answer 2

You could hook into the publish_page transitional status action and use a simple SQL query (via $wpdb) to determine the highest current value of menu_order in the {prefix}_posts table and set the menu_order of the new page accordingly. Example code:

add_action( 'publish_page', 'wpse155926_set_to_last_page', 10, 2 );
function wpse155926_set_to_last_page( $ID, $post ) {
  if ( $post->menu_order === 0 ) {
    global $wpdb;
    $query = "SELECT MAX(menu_order) FROM $wpdb->posts WHERE post_type LIKE 'page' AND post_status LIKE 'publish';";
    $max_menu_order = $wpdb->get_var( $query );
    $post->menu_order = ++$max_menu_order;
    remove_action('publish_page', 'wpse155926_set_to_last_page');
    wp_update_post( $post );
    add_action('publish_page', 'wpse155926_set_to_last_page');
  }
}