Menus

Another common use case you will often need is to query a menu. This is particularly useful for use cases where you will want to control or add items via the backend in the Drupal administration interface.

Add the schema declaration

The first step, as seen in the introduction, is to add the types and fields in the schema. We can do this directly in the schema string in your own schema implementation (src/Plugin/GraphQL/Schema/SdlSchemaMyDrupalGql.php).

...
type Query {
    ...
    menu(name: String!): Menu
    ...
}

type Menu {
  name: String!
  items: [MenuItem]
}

type MenuItem {
  title: String!
  url: Url!
  children: [MenuItem]
}

type Url {
  path: String
}

...

In this schema we can see that we can query a menu by its name. This will return a "Menu" type which includes a name field as well as a list of "MenuItem".

Adding resolvers

To add the resolvers we go to our schema implementation and call the appropriate data producers inside the getResolverRegistry method.

/**
 * {@inheritdoc}
 */
protected function getResolverRegistry() {
  ...

   // Menu query.
  $registry->addFieldResolver('Query', 'menu',
    $builder->produce('entity_load')
      ->map('type', $builder->fromValue('menu'))
      ->map('id', $builder->fromArgument('name'))
  );

  // Menu name.
  $registry->addFieldResolver('Menu', 'name',
    $builder->produce('property_path')
      ->map('type', $builder->fromValue('entity:menu'))
      ->map('value', $builder->fromParent())
      ->map('path', $builder->fromValue('label'))
  );

  // Menu items.
  $registry->addFieldResolver('Menu', 'items',
    $builder->produce('menu_links')
      ->map('menu', $builder->fromParent())
  );

  // Menu title.
  $registry->addFieldResolver('MenuItem', 'title',
    $builder->produce('menu_link_label')
      ->map('link', $builder->produce('menu_tree_link')
        ->map('element', $builder->fromParent()))
  );

  // Menu children.
  $registry->addFieldResolver('MenuItem', 'children',
    $builder->produce('menu_tree_subtree')
      ->map('element', $builder->fromParent())
  );

  // Menu url.
  $registry->addFieldResolver('MenuItem', 'url',
    $builder->produce('menu_link_url')
      ->map('link', $builder->produce('menu_tree_link')
        ->map('element', $builder->fromParent()))
  );

  $registry->addFieldResolver('Url', 'path',
    $builder->produce('url_path')
      ->map('url', $builder->fromParent())
  );

  ...

  return $registry;
}

As we can see here we need to really provide all the fields with a resolver in order to have the data available, this can seem a bit unnecessary at first but it's a crucial step towards a cleaner API. In this case, we resolve the menu inside the Query type and from there we can start resolving each field from Menu and also MenuItem.