wp_unique_term_slug( string $slug, object $term )

Will make slug unique, if it isn’t already.


Description

The $slug has to be unique global to every taxonomy, meaning that one taxonomy term can’t have a matching slug with another taxonomy term. Each slug has to be globally unique for every taxonomy.

The way this works is that if the taxonomy that the term belongs to is hierarchical and has a parent, it will append that parent to the $slug.

If that still doesn’t return an unique slug, then it try to append a number until it finds a number that is truly unique.

The only purpose for $term is for appending a parent, if one exists.


Parameters

$slug

(string) (Required) The string that will be tried for a unique slug.

$term

(object) (Required) The term object that the $slug will belong to.


Return

(string) Will return a true unique slug.


Source

File: wp-includes/taxonomy.php

function wp_unique_term_slug( $slug, $term ) {
	global $wpdb;

	$needs_suffix = true;
	$original_slug = $slug;

	// As of 4.1, duplicate slugs are allowed as long as they're in different taxonomies.
	if ( ! term_exists( $slug ) || get_option( 'db_version' ) >= 30133 && ! get_term_by( 'slug', $slug, $term->taxonomy ) ) {
		$needs_suffix = false;
	}

	/*
	 * If the taxonomy supports hierarchy and the term has a parent, make the slug unique
	 * by incorporating parent slugs.
	 */
	$parent_suffix = '';
	if ( $needs_suffix && is_taxonomy_hierarchical( $term->taxonomy ) && ! empty( $term->parent ) ) {
		$the_parent = $term->parent;
		while ( ! empty($the_parent) ) {
			$parent_term = get_term($the_parent, $term->taxonomy);
			if ( is_wp_error($parent_term) || empty($parent_term) )
				break;
			$parent_suffix .= '-' . $parent_term->slug;
			if ( ! term_exists( $slug . $parent_suffix ) ) {
				break;
			}

			if ( empty($parent_term->parent) )
				break;
			$the_parent = $parent_term->parent;
		}
	}

	// If we didn't get a unique slug, try appending a number to make it unique.

	/**
	 * Filters whether the proposed unique term slug is bad.
	 *
	 * @since WP-4.3.0
	 *
	 * @param bool   $needs_suffix Whether the slug needs to be made unique with a suffix.
	 * @param string $slug         The slug.
	 * @param object $term         Term object.
	 */
	if ( apply_filters( 'wp_unique_term_slug_is_bad_slug', $needs_suffix, $slug, $term ) ) {
		if ( $parent_suffix ) {
			$slug .= $parent_suffix;
		} else {
			if ( ! empty( $term->term_id ) )
				$query = $wpdb->prepare( "SELECT slug FROM $wpdb->terms WHERE slug = %s AND term_id != %d", $slug, $term->term_id );
			else
				$query = $wpdb->prepare( "SELECT slug FROM $wpdb->terms WHERE slug = %s", $slug );

			if ( $wpdb->get_var( $query ) ) {
				$num = 2;
				do {
					$alt_slug = $slug . "-$num";
					$num++;
					$slug_check = $wpdb->get_var( $wpdb->prepare( "SELECT slug FROM $wpdb->terms WHERE slug = %s", $alt_slug ) );
				} while ( $slug_check );
				$slug = $alt_slug;
			}
		}
	}

	/**
	 * Filters the unique term slug.
	 *
	 * @since WP-4.3.0
	 *
	 * @param string $slug          Unique term slug.
	 * @param object $term          Term object.
	 * @param string $original_slug Slug originally passed to the function for testing.
	 */
	return apply_filters( 'wp_unique_term_slug', $slug, $term, $original_slug );
}


Changelog

Changelog
Version Description
WP-2.3.0 Introduced.