Node Blog Featured Image D8 Migration Plugin

NodeBlogFeaturedImage.php

<?php
  
/**
 * @file
 * Contains \Drupal\my_module\Plugin\migrate\source\NodeBlogFeaturedImage.
 */

namespace Drupal\my_module\Plugin\migrate\source;

use Drupal\file\Plugin\migrate\source\d6\File;
use Drupal\Core\Database\Query\Condition;
use Drupal\migrate\Row;

/**
 * Blog Featured Image 
 *
 * @MigrateSource(
 *   id = "my_module_blog_featured_image"
 * )
 */
class NodeBlogFeaturedImage extends File {
  /**
   * {@inheritdoc}
   */
  public function query() {
    $query = $this->select('files', 'f');
    
    // Join data from 'content_type_blog', which is d6's way of storing field data.
    $query->join('content_type_blog', 'ctb', 'ctb.field_blog_feature_img_fid = f.fid');
    
    // Join data from 'node' table
    $query->join('node', 'n', 'n.nid = ctb.nid');
    
    $query->fields('f', ['fid', 'uid', 'filename', 'filepath', 'filemime', 'status', 'timestamp'])
      ->distinct()
      ->condition('n.type', 'blog')
      ->orderBy('n.changed', 'DESC');
    
    return $query;
  }
}