Add menu_link_content support into views

You can easily add the support by implementing hook_entity_type_alter():

/** @var \Drupal\Core\Entity\EntityTypeInterface $menu_link_content */
$menu_link_content = $entity_types['menu_link_content'];
if (!$menu_link_content->hasHandlerClass('views_data')) {
  $menu_link_content->setHandlerClass('views_data', 'Drupal\views\EntityViewsData');
}

But, there is a notice when editing view:
Notice: Undefined index: title in Drupal\views\Plugin\views\HandlerBase->adminLabel() (line 158 of core/modules/views/src/Plugin/views/HandlerBase.php).
It can be fixed by attached patch.

Hi @stefan.r,

I think #2804335: Provide menu item integration for views is closely related and seems to have the same objective. Would you like to read through it, perhaps merge both issues and add your guess about using views_menu_children_filter module as testspace for further implementation and features before writing a patch for core?

We should also discuss the implications from #2315773: Create a menu link field type/widget/formatter if that will ever be done...

What do you think?

Using the patch from #7 plus the hook:

/**
 * Implements hook_entity_type_alter to add views menu-link support (without entity relations):
 *
 * @return void
 */
function MYMODULE_entity_type_alter(array &$entity_types)
{
  /** @var \Drupal\Core\Entity\EntityTypeInterface $menu_link_content */
  $menu_link_content = $entity_types['menu_link_content'];
  if (!$menu_link_content->hasHandlerClass('views_data')) {
    $menu_link_content->setHandlerClass('views_data', 'Drupal\views\EntityViewsData');
  }
}

works to enable views to display menu item entities standalone, BUT the problem is, that entity relationships don't exist with it and that's the main criteria for typical use cases. So menu items don't reference entities and also entities can't reference menu items.
So this is just a very very early starting point or for very simple use cases.

I guess there are two ways to go now:
a) Decide if #2315773: Create a menu link field type/widget/formatter (https://www.drupal.org/project/menu_link in contrib) will happen and if it will, we'd just have to extend what comes from the reference for better usability (see my comment #177 in that issue)

or

b) If the current logic is kept, I'd suggest to extend views_menu_children_filter including #2996145: Support non-content entities to not only support nodes, which wouldn't be enough in the long term view. Based on that module a core patch could be written if the module works well.

How do we proceed and how may decide on #2315773: Create a menu link field type/widget/formatter? Can we ask important core maintainers about that?

In the meantime a solution like #7 can help as quickfix?

With a strong hint from the code in core/modules/block_content/src/BlockContentViewsData.php, using hook_views_data_alter() gives the ability to create a views relationship to the information held in menu_link_content_data.

/**
 * Implements hook_views_data_alter().
 *
 * We need to use this hook instead of hook_views_data() as
 * entity API already provides data for our custom entity type.
 */
function hook_views_data_alter(&$data) {
  // @todo EntityViewsData should add these relationships by default.
  //   https://www.drupal.org/node/2410275
  $data['menu_link_content_field_revision']['id']['relationship']['id'] = 'standard';
  $data['menu_link_content_field_revision']['id']['relationship']['base'] = 'menu_link_content_data';
  $data['menu_link_content_field_revision']['id']['relationship']['base field'] = 'id';
  $data['menu_link_content_field_revision']['id']['relationship']['title'] = t('Menu Link Content ID');
  $data['menu_link_content_field_revision']['id']['relationship']['label'] = t('Get the actual menu link content from a menu link content revision by id.');

  $data['menu_link_content_field_revision']['revision_id']['relationship']['id'] = 'standard';
  $data['menu_link_content_field_revision']['revision_id']['relationship']['base'] = 'menu_link_content_data';
  $data['menu_link_content_field_revision']['revision_id']['relationship']['base field'] = 'revision_id';
  $data['menu_link_content_field_revision']['revision_id']['relationship']['title'] = t('Menu Link Content Revision ID');
  $data['menu_link_content_field_revision']['revision_id']['relationship']['label'] = t('Get the actual menu link content from a menu link content revision by revision id.');
}

Thank you to the person who wrote that code. alexpott ?

Here's a patch that builds on the work from #7 essentially doing away with needing the hook implementation.

Thanks @Steven Jones, looks good, and I think it's okay to set this Needs Review, but please keep in mind that at least in a follow-up issue we need to add relations as written in #11.

I guess this will also needs tests, but didn't check yet, if there are tests for all other views enabled entity types in Core? But I think so...

Created a MR to proceed from #23. Please do NOT create further patches, but instead work on the MR.

#26 missing the additional core/modules/menu_link_content/src/MenuLinkContentViewsData.php

Additional MR for 10.2.x and 11.x had been created.

Sounds interesting!

Will need some test coverage.

MR should be against 11.x too.