Force the WordPress importer to update existing posts instead of skipping them

wordpress-import-update.php

<?php

/**
 * When using the WordPress Importer, update existing 
 * posts instead of skipping them. Updates content according
 * to the import file even if the existing post was updated
 * more recently.
 * 
 * To use, drop this file into your /mu-plugins/ folder or
 * copy this code into your functions.php file.
 */

class WPImporterUpdate {

	protected $existing_post;

	function __construct() {
		add_filter( 'wp_import_existing_post', [ $this, 'wp_import_existing_post' ], 10, 2 );
		add_filter( 'wp_import_post_data_processed', [ $this, 'wp_import_post_data_processed' ], 10, 2 );
	}

	function wp_import_existing_post( $post_id, $post ) {
		if ( $this->existing_post = $post_id ) {
			$post_id = 0; // force the post to be imported
		}
		return $post_id;
	}

	function wp_import_post_data_processed( $postdata, $post ) {
		if ( $this->existing_post ) {
			// update the existing post
			$postdata['ID'] = $this->existing_post;
		}
		return $postdata;
	}

}
new WPImporterUpdate;

Thanks for this code, it is VERY helpful! I reworked it a bit to delete/replace previous meta, and also to ignore if post_type is attachment (because it is very unlikely that they would have been replaced and it takes way longer to load them). If you are interested, my mods are here: https://gist.github.com/ssuess/09efc6431e91a89895ff6b4adf69e643

Thanks for this. it worked like you said it would.

The post's comments were duplicated, not updated. How can I have the comments update instead of duplicate?

Great. its works custom post type also (Y)

two questions...

Does this work for pages as well as posts? Sub-question being if not, any tips on doing that?

And sorry if I overlooked something obvious, but how do I run this? Is it called by using the default /wp-admin/admin.php?import=wordpress

Thanks in advance. Pulling my hair out trying to update pages on import

Thanks this worked great for me. I made this a code snippet to get it to work.