Set the menu link description in hook_entity_presave()

Question

How do I update the menu link description with hook_ENTITY_TYPE_presave()?

I can print out the menu link title and menu link description with the following code.

kint($entity->menu['title']);  
kint($entity->menu['description']);

I only want to update the menu link description when the menu link title is not NULL so the menu link will exist. In fact, I'm wanting to copy the menu link title into the menu link description (when the menu link title is not empty).

The following code updates the node title, but I would like to know how to update the menu link description.

/**
 * Implements hook_ENTITY_TYPE_presave().
 */
function hook_entity_presave(Drupal\Core\Entity\EntityInterface $entity) {
  
  if ($entity->bundle() == 'page') {

    // save a different value as title
    $entity->title = 'New Title';

    // The below outputs the 'title' and 'description' of the menu link
    kint($entity->menu['title']);
    kint($entity->menu['description']);

    // how do I update the menu description?
    // the below doesn't work?
    $entity->menu['description'] = "New menu link description";
    
  }
}

Answer 1

Menu links are entities themselves. Unless you've done something special to create a new menu link entity type, they will be entity type menu_link_content.

You can use hook_ENTITY_TYPE_presave() to make your change. Note that when you see an all-caps section of a hook, that means it should be replaced by a specific value, e.g. hook_node_presave() or hook_menu_link_content_presave(). The difference between these and hook_entity_presave() is that the latter will fire when any entity is saved, while the entity type specific hooks will only fire when an entity of that specific type is saved.

Given all of this, something like the following should work:

// Top of file.
use Drupal\menu_link_content\MenuLinkContentInterface;

/**
 * Ensure that any menu link with a title has a description that matches.
 *
 * Implements hook_ENTITY_TYPE_presave().
 */
MY_MODULE_menu_link_content_presave(MenuLinkContentInterface $menu_link) {
  if (!$menu_link->title->isEmpty()) {
    $menu_link->set('description', $menu_link->title->value);
  }
}