Comment.php

<?php

namespace Drupal\comment\Plugin\migrate\source\d6;

use Drupal\migrate\Row;
use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;

// cspell:ignore vancode

/**
 * Drupal 6 comment source from database.
 *
 * For available configuration keys, refer to the parent classes.
 *
 * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
 * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
 *
 * @MigrateSource(
 *   id = "d6_comment",
 *   source_module = "comment"
 * )
 */
class Comment extends DrupalSqlBase {

  /**
   * {@inheritdoc}
   */
  public function query() {
    $query = $this
      ->select('comments', 'c')
      ->fields('c', [
      'cid',
      'pid',
      'nid',
      'uid',
      'subject',
      'comment',
      'hostname',
      'timestamp',
      'status',
      'thread',
      'name',
      'mail',
      'homepage',
      'format',
    ]);
    $query
      ->innerJoin('node', 'n', '[c].[nid] = [n].[nid]');
    $query
      ->fields('n', [
      'type',
      'language',
    ]);
    $query
      ->orderBy('c.timestamp');
    return $query;
  }

  /**
   * {@inheritdoc}
   */
  public function prepareRow(Row $row) {

    // In D6, status=0 means published, while in D8 means the opposite.
    $row
      ->setSourceProperty('status', !$row
      ->getSourceProperty('status'));

    // If node did not have a language, use site default language as a fallback.
    if (!$row
      ->getSourceProperty('language')) {
      $language_default = $this
        ->variableGet('language_default', NULL);
      $language = $language_default ? $language_default->language : 'en';
      $row
        ->setSourceProperty('language', $language);
    }
    return parent::prepareRow($row);
  }

  /**
   * {@inheritdoc}
   */
  public function fields() {
    return [
      'cid' => $this
        ->t('Comment ID.'),
      'pid' => $this
        ->t('Parent comment ID. If set to 0, this comment is not a reply to an existing comment.'),
      'nid' => $this
        ->t('The {node}.nid to which this comment is a reply.'),
      'uid' => $this
        ->t('The {users}.uid who authored the comment. If set to 0, this comment was created by an anonymous user.'),
      'subject' => $this
        ->t('The comment title.'),
      'comment' => $this
        ->t('The comment body.'),
      'hostname' => $this
        ->t("The author's host name."),
      'timestamp' => $this
        ->t('The time that the comment was created, or last edited by its author, as a Unix timestamp.'),
      'status' => $this
        ->t('The published status of a comment. (0 = Published, 1 = Not Published)'),
      'format' => $this
        ->t('The {filter_formats}.format of the comment body.'),
      'thread' => $this
        ->t("The vancode representation of the comment's place in a thread."),
      'name' => $this
        ->t("The comment author's name. Uses {users}.name if the user is logged in, otherwise uses the value typed into the comment form."),
      'mail' => $this
        ->t("The comment author's email address from the comment form, if user is anonymous, and the 'Anonymous users may/must leave their contact information' setting is turned on."),
      'homepage' => $this
        ->t("The comment author's home page address from the comment form, if user is anonymous, and the 'Anonymous users may/must leave their contact information' setting is turned on."),
      'type' => $this
        ->t("The {node}.type to which this comment is a reply."),
      'language' => $this
        ->t("The {node}.language to which this comment is a reply. Site default language is used as a fallback if node does not have a language."),
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function getIds() {
    $ids['cid']['type'] = 'integer';
    return $ids;
  }

}