reset custom field when navigation menu is deleted in WordPress - php

Question

I have a custom field associated with all posts and pages. It's a dropdown of all the navigation menus.
here is how I'm populating the custom field drop-down: (the field name is custom_menu...)
function acf_load_menu_field_choices( $field ) {
// reset choices
$field['choices'] = array();
$menus = get_terms( 'nav_menu', array( 'hide_empty' => true ) );
$blank_list = json_encode(array( "name" => "Select Menu", "slug" => ""));
$blank_list = json_decode($blank_list);
array_unshift($menus, $blank_list);
foreach ( $menus as $val ) {
$value = $val->slug;
$label = $val->name;
$field['choices'][ $value ] = $label;
}
// return the field
return $field;
}
add_filter('acf/load_field/name=custom_menu', 'acf_load_menu_field_choices');
Here is a common menu location that I'm using on each page:
function register_custom_menu() { //function to register new menu
register_nav_menu('custom-menu',__( 'Custom Menu' ));
}
add_action( 'init', 'register_custom_menu' );
And then I'm assigning a menu dynamically to the location custom-menu based on the custom field menu on each page.
and here is the function the fires on each page when it's loaded:
add_action("wp_ajax_load_custom_menu", "load_custom_menu");
add_action("wp_ajax_nopriv_load_custom_menu", "load_custom_menu");
function load_custom_menu(){
$post_id = $_POST['page_id'];
$page_custom_menu = get_field('custom_menu', $post_id);
if(empty($page_custom_menu) || $page_custom_menu == "primary") return;
$locations = get_theme_mod( 'nav_menu_locations' );
if(!empty($locations)) {
foreach($locations as $locationId => $menuValue) {
if($locationId == "custom-menu") $menu = get_term_by('slug', $page_custom_menu, 'nav_menu');
if(isset($menu)) { $locations[$locationId] = $menu->term_id; }
}
}
set_theme_mod('nav_menu_locations', $locations);
wp_nav_menu( array(
'theme_location' => 'custom-menu',
'menu_id' => 'primary-menu',
'menu_class' => 'main-nav underline-decoration l-to-r-line level-arrows-on outside-item-remove-margin',
'container' => false
)
);
wp_die();
}
This ajax function fires on ready event and recieves a POST value called page_id. This function checks the custom field value of the given page_id for custom-menu and assign that menu to the menu location called custom-menu.
Here's my JavaScript in case you need to have a look on it:
jQuery(document).ready( function($){
let customMenu;
let page_id = script_vars.postID;
$.post(dtLocal.ajaxurl, { action: "load_custom_menu", page_id: page_id }, resp => customMenu = resp);
$(window).scroll(() => {
if(customMenu !== "0"){
$("#phantom .main-nav").remove();
$("#phantom .menu-box").html(customMenu);
}
})
})
This is how my code is working, And everything works fine up to this point.
Now here is the problem
Whenever I delete a Navigation menu from Appearence>Menus>Delete Menu My custom Menu starts behaving unexpectedly because the custom field value is still pointing to the deleted Menu.
What I want to do here is, I want to Delete the Custom Field whenever a menu is deleted. First I want to get the slug of a deleted menu and then find the custom field value with that slug and then finally, delete or reset that custom field.

Answer 1

Menus in WordPress are just terms in a taxonomy. So you can use all of the term hooks.
In particular the pre_delete_term hook.
add_action( 'pre_delete_term', 'my_func' );
function my_func($term, $taxonomy){
// Check the taxonomy is really 'menu', then check term
}

Answer 2

You are looking for action wp_delete_nav_menu that will take one argument - menu id. The problem that at that point your nav menu will be deleted, so you won't be able to take it slug.
If it is possible that you can store nav menu ID instead of slug, that would simplify things greatly.
In acf_load_menu_field_choices replace:
foreach ( $menus as $val ) {
$value = $val->term_id;
$label = $val->name;
$field['choices'][ $value ] = $label;
}
And in load_custom_menu:
$page_custom_menu = get_field('custom_menu', $post_id);
if(empty($page_custom_menu) || $page_custom_menu == /* Should be your primary menu ID */) return;
$locations = get_theme_mod( 'nav_menu_locations' );
if(!empty($locations)) {
foreach($locations as $locationId => $menuValue) {
if($locationId == "custom-menu") $menu = get_term_by('id', $page_custom_menu, 'nav_menu');
if(isset($menu)) { $locations[$locationId] = $menu->term_id; }
}
}
After those changes you will need to rewrite custom_menu in all posts\pages.
After that, following function will remove all related fields when you delete menu. It has been tested only on typical ACF field (string) instead of custom, but should work just fine with your code as well.
add_action('wp_delete_nav_menu', 'delete_all_acf_fields_with_menu', 10, 1);
function delete_all_acf_fields_with_menu($term_id) {
$args = array(
'post_type' => array('post', 'page'),
'posts_per_page' => -1,
'meta_key' => 'custom_menu',
'meta_value' => $term_id,
);
$posts = get_posts($args);
if( $posts ) {
foreach( $posts as $p ) {
delete_field('custom_menu', $p->ID);
}
}
}