class CommentEntityTranslation

class CommentEntityTranslation extends FieldableEntity {
  
  /**
   * {@inheritdoc}
   */
  public function query() {
    $query = $this->select('entity_translation', 'et')
      ->fields('et')
      ->fields('c', [
      'subject',
    ])
      ->condition('et.entity_type', 'comment')
      ->condition('et.source', '', '<>');
    $query->innerJoin('comment', 'c', '[c].[cid] = [et].[entity_id]');
    $query->innerJoin('node', 'n', '[n].[nid] = [c].[nid]');
    $query->addField('n', 'type', 'node_type');
    $query->orderBy('et.created');
    return $query;
  }
  
  /**
   * {@inheritdoc}
   */
  public function prepareRow(Row $row) {
    $cid = $row->getSourceProperty('entity_id');
    $language = $row->getSourceProperty('language');
    $node_type = $row->getSourceProperty('node_type');
    $comment_type = 'comment_node_' . $node_type;
    // Get Field API field values.
    foreach ($this->getFields('comment', $comment_type) as $field_name => $field) {
      // Ensure we're using the right language if the entity is translatable.
      $field_language = $field['translatable'] ? $language : NULL;
      $row->setSourceProperty($field_name, $this->getFieldValues('comment', $field_name, $cid, NULL, $field_language));
    }
    // If the comment subject was replaced by a real field using the Drupal 7
    // Title module, use the field value instead of the comment subject.
    if ($this->moduleExists('title')) {
      $subject_field = $row->getSourceProperty('subject_field');
      if (isset($subject_field[0]['value'])) {
        $row->setSourceProperty('subject', $subject_field[0]['value']);
      }
    }
    return parent::prepareRow($row);
  }
  
  /**
   * {@inheritdoc}
   */
  public function fields() {
    return [
      'entity_type' => $this->t('The entity type this translation relates to'),
      'entity_id' => $this->t('The entity ID this translation relates to'),
      'revision_id' => $this->t('The entity revision ID this translation relates to'),
      'language' => $this->t('The target language for this translation.'),
      'source' => $this->t('The source language from which this translation was created.'),
      'uid' => $this->t('The author of this translation.'),
      'status' => $this->t('Boolean indicating whether the translation is published (visible to non-administrators).'),
      'translate' => $this->t('A boolean indicating whether this translation needs to be updated.'),
      'created' => $this->t('The Unix timestamp when the translation was created.'),
      'changed' => $this->t('The Unix timestamp when the translation was most recently saved.'),
      'subject' => $this->t('The comment title.'),
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function getIds() {
    return [
      'entity_id' => [
        'type' => 'integer',
        'alias' => 'et',
      ],
      'language' => [
        'type' => 'string',
        'alias' => 'et',
      ],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function checkRequirements() {
    parent::checkRequirements();
    if (!$this->moduleExists('comment')) {
      // If we make it to here, the comment module isn't installed.
      throw new RequirementsException('The module comment is not enabled in the source site');
    }
    if (!$this->moduleExists('node')) {
      // Node module is also a requirement.
      throw new RequirementsException('The module node is not enabled in the source site');
    }
  }

}