class ParagraphsItem

class ParagraphsItem extends FieldableEntity {

  /**
   * Join string for getting current revisions.
   *
   * @var string
   */
  const JOIN = "p.revision_id = pr.revision_id";

  /**
   * The prefix of the field table that contains the entity properties.
   *
   * @var string
   */
  const PARENT_FIELD_TABLE_PREFIX = 'field_data_';

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'bundle' => '',
    ] + parent::defaultConfiguration();
  }

  /**
   * {@inheritdoc}
   */
  public function query() {
    $query = $this
      ->select('paragraphs_item', 'p')
      ->fields('p', [
      'item_id',
      'bundle',
      'field_name',
      'archived',
    ])
      ->fields('pr', [
      'revision_id',
    ]);
    $query
      ->innerJoin('paragraphs_item_revision', 'pr', static::JOIN);

    // This configuration item may be set by a deriver to restrict the
    // bundles retrieved.
    if ($this->configuration['bundle']) {
      $query
        ->condition('p.bundle', $this->configuration['bundle']);
    }
    return $query;
  }

  /**
   * {@inheritdoc}
   */
  public function prepareRow(Row $row) {
    [
      'item_id' => $paragraph_id,
      'revision_id' => $paragraph_revision_id,
      'field_name' => $paragraph_parent_field_name,
      'bundle' => $bundle,
    ] = $row
      ->getSource();
    if (!$paragraph_parent_field_name || !is_string($paragraph_parent_field_name)) {
      return FALSE;
    }

    // Get Field API field values.
    foreach (array_keys($this
      ->getFields('paragraphs_item', $bundle)) as $field_name) {
      $row
        ->setSourceProperty($field_name, $this
        ->getFieldValues('paragraphs_item', $field_name, $paragraph_id, $paragraph_revision_id));
    }

    // We have to find the corresponding parent entity (which might be an
    // another paragraph). Active revision only.
    try {
      $parent_data_query = $this
        ->getDatabase()
        ->select(static::PARENT_FIELD_TABLE_PREFIX . $paragraph_parent_field_name, 'fd');
      $parent_data_query
        ->addField('fd', 'entity_type', 'parent_type');
      $parent_data_query
        ->addField('fd', 'entity_id', 'parent_id');
      $parent_data = $parent_data_query
        ->condition("fd.{$paragraph_parent_field_name}_value", $paragraph_id)
        ->condition("fd.{$paragraph_parent_field_name}_revision_id", $paragraph_revision_id)
        ->execute()
        ->fetchAssoc();
    } catch (DatabaseExceptionWrapper $e) {

      // The paragraphs field data|revision table is missing, we cannot get
      // the parent entity identifiers. This is a corrupted database.
      // @todo Shouldn't we have to throw an exception instead?
      return FALSE;
    }
    if (!is_iterable($parent_data)) {

      // We cannot get the parent entity identifiers.
      return FALSE;
    }
    foreach ($parent_data as $property_name => $property_value) {
      $row
        ->setSourceProperty($property_name, $property_value);
    }
    return parent::prepareRow($row);
  }

  /**
   * {@inheritdoc}
   */
  public function fields() {
    $fields = [
      'item_id' => $this
        ->t('The paragraph_item id'),
      'revision_id' => $this
        ->t('The paragraph_item revision id'),
      'bundle' => $this
        ->t('The paragraph bundle'),
      'field_name' => $this
        ->t('The paragraph field_name'),
    ];
    return $fields;
  }

  /**
   * {@inheritdoc}
   */
  public function getIds() {
    return [
      'item_id' => [
        'type' => 'integer',
        'alias' => 'p',
      ],
    ];
  }

}