wpseek.com
A WordPress-centric search engine for devs and theme authors

function update_post_thumbnail_cache( $wp_query = null ) {
	if ( ! $wp_query ) {
		$wp_query = $GLOBALS['wp_query'];
	}

	if ( $wp_query->thumbnails_cached ) {
		return;
	}

	$thumb_ids = array();

	/*
	 * $wp_query may contain an array of post objects or post IDs.
	 *
	 * This ensures the cache is primed for all post objects to avoid
	 * `get_post()` calls in `get_the_post_thumbnail()` triggering an
	 * additional database call for each post.
	 */
	$parent_post_ids = array();
	foreach ( $wp_query->posts as $post ) {
		if ( $post instanceof WP_Post ) {
			$parent_post_ids[] = $post->ID;
		} elseif ( is_int( $post ) ) {
			$parent_post_ids[] = $post;
		}
	}
	_prime_post_caches( $parent_post_ids, false, true );

	foreach ( $wp_query->posts as $post ) {
		$id = get_post_thumbnail_id( $post );
		if ( $id ) {
			$thumb_ids[] = $id;
		}
	}

	if ( ! empty( $thumb_ids ) ) {
		_prime_post_caches( $thumb_ids, false, true );
	}

	$wp_query->thumbnails_cached = true;
}