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');
        }
    }

}