Address fatal error in Action Scheduler when identity field was not correctly set on migration

fix-as-action-ids.php

<?php
/*
Plugin Name: Fix Action Scheduler Action IDs
Version: 0.2
Author: Automattic
Author URI: https://automattic.com/
Description: This is a one time use plugin designed to address a fatal error during AS migration where the identity field in the actionscheduler_actions table did not get set before actions were migrated.

License: GNU General Public License v3.0 (or later)
License URI: http://www.opensource.org/licenses/gpl-license.php
*/

add_action( 'init', function() {
	global $wpdb;
	// Assign table names with AS inactive.
	$action_table = $wpdb->prefix . 'actionscheduler_actions';
	$log_table    = $wpdb->prefix . 'actionscheduler_logs';
	// Get the relevant option.
	$demarkation_id = get_option( 'action_scheduler_hybrid_store_demarkation' );
	// Or get the maximum action ID in the posts table.
	if ( $demarkation_id < 3 ) {
		$demarkation_id = $wpdb->get_var( $wpdb->prepare( "SELECT MAX(ID) FROM {$wpdb->posts} WHERE post_type = %s", 'scheduled-action' ) );
		$demarkation_id++;
	}
	// If there isn't a demarkation ID then there is nothing to do.
	if ( $demarkation_id < 3 ) {
		return;
	}
	// Check for a lower action ID in the actions table.
	$min_action_id = $wpdb->get_var( "SELECT MIN(action_id) FROM {$action_table}" );
	if ( $min_action_id < $demarkation_id ) {
		$max_action_id = $wpdb->get_var( "SELECT MAX(action_id) FROM {$action_table}" );
		// Update the action IDs to a range that doesn't currently exist.
		$increase = max( $max_action_id + 1, $demarkation_id + 1 );
		$wpdb->query( $wpdb->prepare( "UPDATE {$action_table} SET action_id = action_id + %d", $increase ) );
		$wpdb->query( $wpdb->prepare( "UPDATE {$log_table} SET action_id = action_id + %d", $increase ) );
	}
});