ElasticPress: Add specific post meta to search fields

elasticpress-add-meta-fields-to-search.php

<?php
add_filter(
	'ep_weighting_configuration_for_search',
	function( $weighting_config ) {
		global $wpdb;
		$post_meta = get_transient( 'custom_ep_distinct_post_meta' );

		if ( ! $post_meta ) {
			$post_meta = $wpdb->get_col(
				"SELECT DISTINCT meta_key
				FROM {$wpdb->postmeta} pm 
				LEFT JOIN {$wpdb->posts} p ON pm.post_id = p.ID
				WHERE meta_key like 'mdl_modules_%_text'"
			);

			set_transient( 'custom_ep_distinct_post_meta', $post_meta );
		}

		foreach ( $weighting_config as $post_type => $fields ) {
			foreach ( $post_meta as $meta_key ) {
				$weighting_config[ $post_type ][ "meta.{$meta_key}.value" ] = [
					'enabled' => 1,
					'weight'  => 10,
				];
			}
		}
		return $weighting_config;
	}
);

add_action(
	'update_postmeta',
	function( $meta_id, $object_id, $meta_key ) {
		if ( preg_match( '/mdl_modules_([0-9]*)_text/', $meta_key ) ) {
			delete_transient( 'custom_ep_distinct_post_meta' );
		}
	},
	10,
	3
);