Custom Post Types with taxonomy in the permalink

custom-cpt.php

<?php
/*
In this example, I've created custom post-types called "locations" and custom taxonomy called "state"
By default the generated permalink structure would look like this:
Locations: <base-url>/locations/<post-slug>/
State: <base-url>/state/<taxonomy-slug>/

But here is what I wanted:
1. Replace "locations" with "service-areas" in the permalink for locaitons.
2. Permalink structure for "locations" to be: <base-url>/service-areas/<state-slug>/<locations-slug>
      Example: <base-url>/service-areas/sa/adelaide/
3. Permalink structure for "state" to be: <base-url>/service-areas/<state-slug>/
      Example: <base-url>/service-areas/sa/
4. Permalink structure for "locations" archive to be : <base-url>/service-areas/

Note: The advantage of using this permalink structures. It has a flow to these URLs
*/

/*Custom Post Types*/

/**
 * Register a Custom post type.
 *
 * @link http://codex.wordpress.org/Function_Reference/register_post_type
 * @link https://developer.wordpress.org/resource/dashicons
 */

//Use this as an example as required
add_action( 'init', 'krish_locations_init' );
function krish_locations_init() {
	$labels = array(
		'name'               => _x( 'Locations', 'post type general name', 'krish-cpt' ),
		'singular_name'      => _x( 'Locations', 'post type singular name', 'krish-cpt' ),
		'menu_name'          => _x( 'Locations', 'admin menu', 'krish-cpt' ),
		'name_admin_bar'     => _x( 'Location', 'add new on admin bar', 'krish-cpt' ),
		'add_new'            => _x( 'Add New', 'location', 'krish-cpt' ),
		'add_new_item'       => __( 'Add New Location', 'krish-cpt' ),
		'new_item'           => __( 'New Location', 'krish-cpt' ),
		'edit_item'          => __( 'Edit Location', 'krish-cpt' ),
		'view_item'          => __( 'View Location', 'krish-cpt' ),
		'all_items'          => __( 'All Locations', 'krish-cpt' ),
		'search_items'       => __( 'Search Locations', 'krish-cpt' ),
		'parent_item_colon'  => __( 'Parent Location:', 'krish-cpt' ),
		'not_found'          => __( 'No locations found.', 'krish-cpt' ),
		'not_found_in_trash' => __( 'No locations found in Trash.', 'krish-cpt' )
	);
	$args   = array(
		'labels'             => $labels,
		//'description'        => __( '', 'krish-cpt' ), //update description if necessary or call custom field
		'public'             => TRUE,
		'publicly_queryable' => TRUE,
		'show_ui'            => TRUE,
		'show_in_menu'       => TRUE,
		'menu_icon'          => 'dashicons-location-alt',
		'query_var'          => TRUE,
		'rewrite'            => array( 'with_front' => FALSE, 'slug' => 'service-areas/%state%' ),
		'capability_type'    => 'post',
		'has_archive'        => 'service-areas',
		'hierarchical'       => TRUE,
		'menu_position'      => NULL,
		'supports'           => array( 'title', 'content', 'thumbnail', 'revisions', 'page-attributes' )
	);
	register_post_type( 'locations', $args );
}


/*Custom Taxonomies*/

/*
 * Register a Custom Taxonomy
 *
 * @link https://codex.wordpress.org/Function_Reference/register_taxonomy
 *
 */

//Use this as an example as required
add_action( 'init', 'krish_init_state' );
function krish_init_state() {
	$labels      = array(
		"name"          => __( "States", "krish-cpt" ),
		"singular_name" => __( "State", "krish-cpt" ),
	);
	$args        = array(
		"label"                 => __( "States", "krish-cpt" ),
		"labels"                => $labels,
		"public"                => TRUE,
		"publicly_queryable"    => TRUE,
		"hierarchical"          => TRUE,
		"show_ui"               => TRUE,
		"show_in_menu"          => TRUE,
		"show_in_nav_menus"     => TRUE,
		"query_var"             => TRUE,
		"rewrite"               => array( 'with_front' => FALSE, 'slug' => 'service-areas' ),
		"show_admin_column"     => TRUE,
		"show_in_rest"          => TRUE,
		"rest_base"             => "state",
		"rest_controller_class" => "WP_REST_Terms_Controller",
		"show_in_quick_edit"    => TRUE,
	);
	$related_cpt = array( "locations" ); //change post-types as required
	register_taxonomy( "state", $related_cpt, $args );
}


/* ===== Locations CPT permalink's %state% to be replaced by state taxonomy value ===== */
add_filter( 'post_type_link', 'locations_post_link', 1, 3 );
function locations_post_link( $post_link, $id = 0 ) {
	$post  = get_post( $id );
	$terms = wp_get_object_terms( $post->ID, 'state' );
	if ( $terms ) {
		return str_replace( '%state%', $terms[0]->slug, $post_link );
	}
	
	return $post_link;
}
?>