wp_check_post_hierarchy_for_loops() WP 3.1.0

Check the given subset of the post hierarchy for hierarchy loops.

Prevents loops from forming and breaks those that it finds. Attached to the 'wp_insert_post_parent' filter.

No Hooks.

Return

Int. The new post_parent for the post, 0 otherwise.

Usage

wp_check_post_hierarchy_for_loops( $post_parent, $post_ID );

$post_parent(int) (required)

ID of the parent for the post we're checking.

$post_ID(int) (required)

ID of the post we're checking.

Code of wp check post hierarchy for loops: wp-includes/post.php ^{WP 5.2.2}

<?php
function wp_check_post_hierarchy_for_loops( $post_parent, $post_ID ) {
	// Nothing fancy here - bail.
	if ( ! $post_parent ) {
		return 0;
	}

	// New post can't cause a loop.
	if ( empty( $post_ID ) ) {
		return $post_parent;
	}

	// Can't be its own parent.
	if ( $post_parent == $post_ID ) {
		return 0;
	}

	// Now look for larger loops.
	if ( ! $loop = wp_find_hierarchy_loop( 'wp_get_post_parent_id', $post_ID, $post_parent ) ) {
		return $post_parent; // No loop
	}

	// Setting $post_parent to the given value causes a loop.
	if ( isset( $loop[ $post_ID ] ) ) {
		return 0;
	}

	// There's a loop, but it doesn't contain $post_ID. Break the loop.
	foreach ( array_keys( $loop ) as $loop_member ) {
		wp_update_post(
			array(
				'ID'          => $loop_member,
				'post_parent' => 0,
			)
		);
	}

	return $post_parent;
}