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wp_check_post_hierarchy_for_loops( int $post_parent, int $post_ID )

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

Description

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

See also

Parameters

$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.

Return

(int) The new post_parent for the post, 0 otherwise.

Source

File: wp-includes/post.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.
	$loop = wp_find_hierarchy_loop( 'wp_get_post_parent_id', $post_ID, $post_parent );
	if ( ! $loop ) {
		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;
}

Uses

Uses Description
wp-includes/functions.php: wp_find_hierarchy_loop()

Find hierarchy loops using a callback function that maps object IDs to parent IDs.
wp-includes/post.php: wp_update_post()

Update a post with new post data.

Changelog

Version Description
3.1.0 Introduced.

© 2003–2019 WordPress Foundation
Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/functions/wp_check_post_hierarchy_for_loops