WordPress at a glance
function is not described

update_object_term_cache() WP 2.3.0

Updates the cache for the given term object ID(s).

Note: Due to performance concerns, great care should be taken to only update term caches when necessary. Processing time can increase exponentially depending on both the number of passed term IDs and the number of taxonomies those terms belong to.

Caches will only be updated for terms not already cached.

No Hooks.

Return

null/false. False if all of the terms in $object_ids are already cached.

Usage

update_object_term_cache( $object_ids, $object_type );
$object_ids(string/int[]) (required)
Comma-separated list or array of term object IDs.
$object_type(string/string[]) (required)
The taxonomy object type or array of the same.

Changelog

Since 2.3.0 Introduced.

Code of update_object_term_cache() WP 5.5.1

<?php
function update_object_term_cache( $object_ids, $object_type ) {
	if ( empty( $object_ids ) ) {
		return;
	}

	if ( ! is_array( $object_ids ) ) {
		$object_ids = explode( ',', $object_ids );
	}

	$object_ids     = array_map( 'intval', $object_ids );
	$non_cached_ids = array();

	$taxonomies = get_object_taxonomies( $object_type );

	foreach ( $taxonomies as $taxonomy ) {
		$cache_values = wp_cache_get_multiple( (array) $object_ids, "{$taxonomy}_relationships" );

		foreach ( $cache_values as $id => $value ) {
			if ( false === $value ) {
				$non_cached_ids[] = $id;
			}
		}
	}

	if ( empty( $non_cached_ids ) ) {
		return false;
	}

	$non_cached_ids = array_unique( $non_cached_ids );

	$terms = wp_get_object_terms(
		$non_cached_ids,
		$taxonomies,
		array(
			'fields'                 => 'all_with_object_id',
			'orderby'                => 'name',
			'update_term_meta_cache' => false,
		)
	);

	$object_terms = array();
	foreach ( (array) $terms as $term ) {
		$object_terms[ $term->object_id ][ $term->taxonomy ][] = $term->term_id;
	}

	foreach ( $non_cached_ids as $id ) {
		foreach ( $taxonomies as $taxonomy ) {
			if ( ! isset( $object_terms[ $id ][ $taxonomy ] ) ) {
				if ( ! isset( $object_terms[ $id ] ) ) {
					$object_terms[ $id ] = array();
				}
				$object_terms[ $id ][ $taxonomy ] = array();
			}
		}
	}

	foreach ( $object_terms as $id => $value ) {
		foreach ( $value as $taxonomy => $terms ) {
			wp_cache_add( $id, $terms, "{$taxonomy}_relationships" );
		}
	}
}