MenuLink vs MenuLinkContent - what's the point?

Question

I'm struggling to figure out relationship between MenuLink and MenuLinkContent.

I'm creating new menu item like:

$menuItem = MenuLinkContent::create($params);

I can also query those elements like:

$menuItems = \Drupal::entityTypeManager()->getStorage('menu_link_content')->loadByProperties(['link.uri' => "internal:$path"]);

And that works well. Now if I need one of those object I want to get it's "siblings" - other object that share same parent. I have some weird structure:

$this->menuLinkManager = \Drupal::service('plugin.manager.menu.link');
$parentId = $menuItem->getParentId();
$parent = $this->menuLinkManager->createInstance($this->menuLinkManager->getDefinition($parentId)['id']);

And here I'm getting it's parent, but it's not MenuLinkContent object any more but instance of MenuLinkInterface. It has some fields as MenuLinkContent, but not all. I.e. I don't know how to get link path and similar.

There I can go further:

$siblings = $this->menuLinkManager->getChildIds($parent->getPluginId());

But main question is how to get MenuLinkContent when I have that MenuLinkInterface object?

Sub-question - why oh why is needed this parallel menu system and parallel menu classes?

Answer 1

$siblings = $this->menuLinkManager->getChildIds($parent->getPluginId());

But main question is how to get MenuLinkContent when I have that MenuLinkInterface object?

There are two types of plugin IDs. Without or with a colon :.

Non-derived plugins

Without they point directly to a single plugin definition.

For example the admin menu

\Drupal::service('plugin.manager.menu.link')->getChildIds('system.admin');

consists mainly of non-derived menu links which IDs you find in *.links.menu.yml files.

Derived plugins

With colon the first part is the base plugin ID and the second part is the derivative ID.

For example, if you have created a multi-level main menu from UI and apply this command on a menu parent

\Drupal::service('plugin.manager.menu.link')->getChildIds('standard.front_page');

You get links like this

menu_link_content:421a421a-cb1d-33e7-a810-1e7341f7906b

for the base plugin MenuLinkContent (BTW also defined in a YAML file) with a deriver for MenuLinkContent entities (identified by UUID).

$entity = \Drupal::service('entity.repository')
  ->loadEntityByUuid('menu_link_content', '421a421a-cb1d-33e7-a810-1e7341f7906b');

If you have already a plugin instance you can get the UUID from the plugin object. See https://drupal.stackexchange.com/a/235769/47547