Added entity reference layout revisions plugin.

[dasjo]

Based on #909, I added a similar plugin for entity reference layout revisions.
https://www.drupal.org/project/entity_reference_layout

This works for me to access the data from paragraph fields, what is still missing is exposing any layout information.

Because it took a me a while to figure out how to draft the schema, also sharing the code I am currently using for it. Maybe for later reference:

schema file

schema {
  query: Query
}

type Query {
  article(id: Int!): Article
  articles(
    offset: Int = 0
    limit: Int = 10
  ): ArticleConnection!
}

type Article {
  id: Int!
  title: String!
  author: String
  body: String
  contents: [ListItem]!
}

interface ListItem {
  id: Int!
}

type SectionItem implements ListItem {
  id: Int!
}

type ProductItem implements ListItem {
  id: Int!
  title: String!
  body: String
  product_reference_id: String
}

type TextItem implements ListItem {
  id: Int!
  text: String!
}

type ArticleConnection {
  total: Int!
  items: [Article!]
}

Schema class

  /**
   * {@inheritdoc}
   */
  public function getResolverRegistry() {
    $builder = new ResolverBuilder();
    $registry = new ResolverRegistry();

    $this->addQueryFields($registry, $builder);
    $this->addArticleFields($registry, $builder);

    // Re-usable connection type fields.
    $this->addConnectionFields('ArticleConnection', $registry, $builder);

    return $registry;
  }

  /**
   * @param \Drupal\graphql\GraphQL\ResolverRegistry $registry
   * @param \Drupal\graphql\GraphQL\ResolverBuilder $builder
   */
  protected function addArticleFields(ResolverRegistry $registry, ResolverBuilder $builder) {
    $registry->addFieldResolver('Article', 'id',
      $builder->produce('entity_id')
        ->map('entity', $builder->fromParent())
    );

    $registry->addFieldResolver('Article', 'title',
      $builder->produce('entity_label')
        ->map('entity', $builder->fromParent())
    );

    $registry->addFieldResolver('Article', 'author',
      $builder->compose(
        $builder->produce('entity_owner')
          ->map('entity', $builder->fromParent()),
        $builder->produce('entity_label')
          ->map('entity', $builder->fromParent())
      )
    );

    $registry->addFieldResolver('Article', 'body',
      $builder->produce('property_path')
        ->map('type', $builder->fromValue('entity:node'))
        ->map('value', $builder->fromParent())
        ->map('path', $builder->fromValue('body.value'))
    );

    $registry->addFieldResolver('Article', 'contents',
      $builder->produce('entity_reference_layout_revisions')
        ->map('entity', $builder->fromParent())
        ->map('field', $builder->fromValue('field_contents'))
    );

    $registry->addTypeResolver('ListItem', function ($value) {
      if ($value instanceof Paragraph) {
        switch ($value->bundle()) {
          case 'section': return 'SectionItem';
          case 'product_item': return 'ProductItem';
          case 'text': return 'TextItem';
        }
      }
      throw new Error('Could not resolve ListItem type.');
    });
    
    // Helps traverse from paragraph over entity reference to the field values.
    $productItemBuilder = $builder->compose(
      $builder->produce('entity_reference')
        ->map('entity', $builder->fromParent())
        ->map('field', $builder->fromValue('field_product')),
      $builder->produce('seek')
        ->map('input', $builder->fromParent())
        ->map('position', $builder->fromValue(0))
    );

    $registry->addFieldResolver('ProductItem', 'id',
      $builder->compose(
        $productItemBuilder,
        $builder->produce('entity_id')
          ->map('entity', $builder->fromParent())
      )
    );

    $registry->addFieldResolver('ProductItem', 'title',
      $builder->compose(
        $productItemBuilder,
        $builder->produce('entity_label')
          ->map('entity', $builder->fromParent())
      )
    );

    $registry->addFieldResolver('ProductItem', 'body',
      $builder->compose(
        $productItemBuilder,
        $builder->produce('property_path')
          ->map('type', $builder->fromValue('entity:node'))
          ->map('value', $builder->fromParent())
          ->map('path', $builder->fromValue('body.value'))
      )
    );

    $registry->addFieldResolver('ProductItem', 'product_reference_id',
      $builder->compose(
        $productItemBuilder,
        $builder->produce('property_path')
          ->map('type', $builder->fromValue('entity:node'))
          ->map('value', $builder->fromParent())
          ->map('path', $builder->fromValue('field_product_reference_id.value'))
      )
    );

    $registry->addFieldResolver('TextItem', 'id',
      $builder->produce('entity_id')
        ->map('entity', $builder->fromParent())
    );

    $registry->addFieldResolver('TextItem', 'text',
      $builder->produce('property_path')
        ->map('type', $builder->fromValue('entity:paragraph'))
        ->map('value', $builder->fromParent())
        ->map('path', $builder->fromValue('field_text.value'))
    );
  }

  /**
   * @param \Drupal\graphql\GraphQL\ResolverRegistry $registry
   * @param \Drupal\graphql\GraphQL\ResolverBuilder $builder
   */
  protected function addQueryFields(ResolverRegistry $registry, ResolverBuilder $builder) {
    $registry->addFieldResolver('Query', 'article',
      $builder->produce('entity_load')
        ->map('type', $builder->fromValue('node'))
        ->map('bundles', $builder->fromValue(['article']))
        ->map('id', $builder->fromArgument('id'))
    );

    $registry->addFieldResolver('Query', 'articles',
      $builder->produce('query_articles')
        ->map('offset', $builder->fromArgument('offset'))
        ->map('limit', $builder->fromArgument('limit'))
    );
  }

  /**
   * @param string $type
   * @param \Drupal\graphql\GraphQL\ResolverRegistry $registry
   * @param \Drupal\graphql\GraphQL\ResolverBuilder $builder
   */
  protected function addConnectionFields($type, ResolverRegistry $registry, ResolverBuilder $builder) {
    $registry->addFieldResolver($type, 'total',
      $builder->callback(function (HeadlessConnection $connection) {
        return $connection->total();
      })
    );

    $registry->addFieldResolver($type, 'items',
      $builder->callback(function (HeadlessConnection $connection) {
        return $connection->items();
      })
    );
  }

[codecov]

Codecov Report

Merging #968 into 8.x-4.x will decrease coverage by 1.46%.
The diff coverage is 0%.

@@              Coverage Diff              @@
##             8.x-4.x     #968      +/-   ##
=============================================
- Coverage      62.03%   60.57%   -1.47%     
- Complexity       537      558      +21     
=============================================
  Files             95       96       +1     
  Lines           1367     1400      +33     
=============================================
  Hits             848      848              
- Misses           519      552      +33

Impacted Files	Coverage Δ	Complexity Δ
...aProducer/Field/EntityReferenceLayoutRevisions.php	0% <0%> (ø)	21 <21> (?)

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