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;

great function balbuf just a question, Do you know why the wp:meta_key are not updating?

@pardocorp I think it might be because wordpress-importer uses add_post_meta instead of update_post_meta, so it's creating new postmeta entries. (see source code L836).

@brucevdkooij @pardocorp I think that's correct, so assuming the post meta contained in the import file is complete for each post, you'd have to just clear out all existing post meta first (which could be done inside of this if block: https://gist.github.com/balbuf/d232769f1e7d66fe91b8ecd7795ef3cb#file-wordpress-import-update-php-L23-L25). It doesn't look like there is any other way to get the importer to use update_post_meta instead of add_post_meta

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?