Media

Image, File, Gallery (and the Featured image target) store attachment IDs. The Media library item by ID, URL or file path transformation finds them:

All values of a batch are found with at most two queries. Nothing is found for URLs of other sites or paths outside the uploads folder.

#Files that are not in the media library yet

The Connector never downloads files by itself: fetching arbitrary URLs from a migration file would let a file make your server request anything. Two safe ways:

1. Copy the old uploads into wp-content/uploads and register them (for example wp media import in WP-CLI), then use the lookup above.
2. Write a transformation that downloads from hosts you allow:

use Cybo\AdvancedFieldEngine\Connector\Transform\TransformFailed;

add_action( 'cafe_register_migration_transformers', function () {
	cafe_register_migration_transformer(
		'download_old_site_image',
		'Download from old.example.com',
		function ( $url, array $options, $context ) {
			if ( ! $url || 'old.example.com' !== wp_parse_url( $url, PHP_URL_HOST ) ) {
				throw new TransformFailed( 'Only images of old.example.com are downloaded.' );
			}

			if ( $context->dry_run ) {
				return null; // Never download while checking.
			}

			require_once ABSPATH . 'wp-admin/includes/media.php';
			require_once ABSPATH . 'wp-admin/includes/file.php';
			require_once ABSPATH . 'wp-admin/includes/image.php';

			$id = media_sideload_image( esc_url_raw( $url ), 0, null, 'id' );

			if ( is_wp_error( $id ) ) {
				throw new TransformFailed( $id->get_error_message() );
			}

			return $id;
		}
	);
} );

Downloaded files are not removed by a rollback.

#Checks

CAFE's field types check the attachment on save: it must exist, and its MIME type must be allowed by the field (Image: images; File: the field's allowed types). A missing or wrong attachment makes the record invalid, with the field and the reason in the report.