Using a Parent > Child category structure with duplicate child url slugs; for urls like `category/parent-1/child` and `category/parent-2/child`.

duplicate-child-term-url-structure.php

<?php
/**
 * Plugin Name: Duplicated Child Term Url Slugs
 * Description: Duplicate child term urls slugs in hierarchical taxonomies.
 * Version: 0.1.0
 * Author: joshuadnelson
 * License: GPLv2 or later
 * License URI: https://www.gnu.org/licenses/gpl-2.0.html
 *
 * This is setup like a plugin, but can be included in a theme or as a class in a plugin.
 *
 * Using a Parent > Child category structure with duplicate child url slugs;
 * for urls like `category/parent-1/child` and `category/parent-2/child`.
 *
 * Child term slugs must be unique per WordPress core requirements.
 * In order to have duplicated child url slugs, the term slug must follow
 * a pattern we can transform to tell WordPress how to route the url.
 *
 * Then apply a custom rewrite rule to match the pattern and filter the
 * term link to remove the parent term slug from the child term url.
 *
 * Here the child slugs are structured like "{parent-slug}_{child-url-slug}"
 * and the term link is shown as `category/{parent-slug}/{child-url-slug}`.
 *
 * Examples:
 *     - url `example.url/category/books/hobbit/`
 *         for the `books_hobbit` child term and `books` parent term
 *     - url `example.url/category/movies/hobbit/`
 *         for the `movies_hobbit` child term and `movies` parent term
 *
 * Notes:
 *   - Permalinks need to be "pretty" and need to be flushed after apply these changes.
 *   - Parent terms must be unique, child terms can be duplicated.
 *   - Terms cannot have a "_" in a slug other than for this purpose.
 *   - Child terms must contain the parent term slug, be careful if you change those on
 *     the parent term you will need to update the child term slugs as well.
 *   - Only works for hierarchical taxonomies, specifically the built-in 'category' taxonomy.
 *     You can modify the taxonomy name in the code to work with other taxonomies
 *     by changing the 'category' taxonomy name and the 'category_name' query var.
 */

/**
 * Main class for the Duplicated Child Url Slugs plugin.
 *
 * @since 0.1.0
 */
class DuplicatedChildUrlSlugs {

	/**
	 * The taxonomy name.
	 *
	 * @since 0.1.0
	 * @var string
	 */
	protected $taxonomy = 'category';

	/**
	 * The taxonomy query var.
	 *
	 * @since 0.1.0
	 * @var string
	 */
	protected $query_var = 'category_name';

	/**
	 * The separator used to separate parent and child term slugs.
	 *
	 * @since 0.1.0
	 * @var string
	 */
	protected $sep = '_';

	/**
	 * Register the plugin
	 *
	 * @since 0.1.0
	 * @return void
	 */
	public function register() {

		// Filter the term link to handle hierarchical taxonomy permalinks.
		add_filter( 'term_link', array( $this, 'term_link' ), 10, 3 );

		// Parse the query to handle hierarchical taxonomy permalinks.
		add_action( 'parse_query', array( $this, 'parse_query' ) );

		// Add custom rewrite rules for parent/child category urls.
		add_action( 'init', array( $this, 'rewrite_rules' ), 100 );

	}

	/**
	 * Add custom rewrite rules for parent/child category urls.
	 *
	 * Adds a rewrite rule that will match terms
	 * that have their slug prefixed with the parent term
	 * slug, separated by an underscore, but their url
	 * is just the child term slug.
	 *
	 * @since 0.1.0
	 * @return void
	 */
	function rewrite_rules() {

		$tax_obj = get_taxonomy( $this->taxonomy );

		if ( $tax_obj ) {
			$tax_slug = $tax_obj->rewrite['slug'];
			add_rewrite_rule(
				$tax_obj->rewrite['slug'] . '/([^/]+)/([^/]+)/?',
				'index.php?' . $tax_obj->query_var . '=$matches[1]_$matches[2]',
				'top'
			);
		}
	}

	/**
	 * Filter the term link to handle hierarchical taxonomy permalinks.
	 *
	 * This will filter the term link to remove the parent term slug
	 * from the child term url, so that the url is just the child term slug,
	 * where the child term name is "parent_child" and the parent term name is "parent".
	 *
	 * @since 0.1.0
	 * @param string $link The term link
	 * @param WP_Term $term The term object
	 * @param string $taxonomy The taxonomy name
	 * @return string
	 */
	function term_link( $link, $term, $taxonomy ) {

		if ( $taxonomy !== $this->taxonomy ) {
			return $link;
		}

		// Get the parent term
		$parent_term = get_term( $term->parent, $taxonomy );

		if ( $parent_term && ! is_wp_error( $parent_term ) ) {
			// Remove the "parent_" prefix from the child term slug
			// to generate a url that looks like /parent/child/
			$link = str_replace( '/' . $term->slug, '/' . str_replace ( $parent_term->slug . '_', '', $term->slug ), $link );
		}

		return $link;
	}

	/**
	 * Parse the query to handle hierarchical taxonomy permalinks.
	 *
	 * This filter the query to check for terms that are child terms
	 * yet do not have the parent term in the slug, thus the parent/child
	 * structure should literally look for a "child" slug, not "parent_child"
	 *
	 * @since 0.1.0
	 * @param WP_Query $query The WP_Query instance (passed by reference)
	 * @return void
	 */
	function parse_query( $query ) {

		// Check if we have the taxonomy query var set.
		if ( isset( $query->query_vars[ $this->query_var ] ) ) {

			// If we have a term slug with a separator, check if it's a child term
			$slug = $query->query_vars[ $this->query_var ];
			if ( strpos( $slug, $this->sep ) !== false ) {

				// Separate the parent and child term slugs.
				list( $parent, $child ) = explode( $this->sep, $slug, 2 );

				// If the parent-child term does not exist, but the child term
				// slug as-is is valid, then set the query var to the child term.
				if ( ! term_exists( $slug, $this->taxonomy ) && term_exists( $child, $this->taxonomy ) ) {
					$query->query_vars[ $this->query_var ] = $child;
				}
			}
		}
	}
}

$dup_url_slugs = new DuplicatedChildUrlSlugs();
$dup_url_slugs->register();

For a custom taxonomy, set the $taxonomy var as your taxonomy slug and $query_var with your taxonomy's query variable (see register_taxonomy)

Hello, first of all, thank you for your plugin. I'm trying to do it for woocommerce product categories but I couldn't do it. Can you help me? Example of the URL structure I want to use

curtain/rooms/living-room/
wall-murals/rooms/living-room/

Have a nice day

Hey @sergenadiyaman. You're example needs to account for two modifications: a custom taxonomy and another level of duplication in the url slug - nesting 3-terms deep instead of 2-terms deep.

Custom taxonomy: product_cat

This example is for the built-in category taxonomy, you'll need to make some changes to use this on custom taxonomies.

I believe WooCommerce "product categories" are registered as product_cat, so you'll first want set $taxonomy = 'product_cat' and also $query_var = 'product_cat' (I'm not 100% sure on the WooCommerce naming for this, but the taxonomy slug is usually the default query_var).

Additional level to the url pattern

This is more complicated. You'll also need to update this to support 3-levels of nested permalink structure, this gist adds support for two levels (/parent/child/) but your example has three (/grandparent/parent/child/), which means the rewrite rule needs to look at three different parts of the link and you'll need a consistent term slug pattern to match to the correct grandparent, parent, and child terms.

For instance you may need to name each of those terms as:

• curtain + curtain_rooms + curtain_rooms_living-room to support a url like /curtain/rooms/living-room/
• wall-murals + wall-murals_rooms + wall-murals_rooms_living-room to support a url like wall-murals/rooms/living-room/

...and then parse that permalink to match the terms accordingly, some like this (warning I have not tested this):

function rewrite_rules() {

	$tax_obj = get_taxonomy( $this->taxonomy );

	if ( $tax_obj ) {
		$tax_slug = $tax_obj->rewrite['slug'];
		add_rewrite_rule(
			$tax_obj->rewrite['slug'] . '/([^/]+)/([^/]+)/([^/]+)/?',
			'index.php?' . $tax_obj->query_var . '=$matches[1]_$matches[2]_$matches[3]',
			'top'
		);
	}
}

You'll also need to update the logic in the term_link filter to look for a grandparent term & update the url. Lastly, the parse_query would need to be updated as well, to accommodate terms not matching these patterns. Best of luck!

I'm sorry, I'm not a software developer. I'm just trying to make my website more efficient and I discovered your plugin. It works for post types, but I couldn't do it for Woocommerce product categories. I have no idea which taxamony to change or how to update term_link. I would appreciate it if you could write more clearly. Or it would be great if you could make a new plugin like the one you made. Thank you for your help

To get this gist working with WooCommerce you should only need to change two lines:

• Line 55 from protected $taxonomy = 'category'; to protected $taxonomy = 'product_cat';
• Line 63 from protected $query_var = 'category_name'; to protected $query_var = 'product_cat';.

However, that will still only work for a 2-level permalink structure like rooms\living-rooms. Going to a 3-level permalink structure like curtain/rooms/living-room/ is outside of the scope of this plugin as it's currently written.

thanks for your help