Modify post permalinks

modify-post-permalinks.php

<?php

add_action('registered_post_type', 'make_posts_hierarchical', 10, 2);

function make_posts_hierarchical($post_type, $pto)
{
    if ($post_type != 'post') return; // Return, if not post type posts

    global $wp_post_types; // access $wp_post_types global variable

    $wp_post_types['post']->hierarchical = 1; // Set post type "post" to be hierarchical

    // add_post_type_support('post', 'page-attributes');  // Add page attributes to post backend
}


add_filter('post_link', 'add_parent_child_cat_in_post_permalink', 10, 3);
// add_filter('pre_post_link', 'add_parent_child_cat_in_post_permalink', 10, 3);
function add_parent_child_cat_in_post_permalink($permalink, $post, $leavename)
{
    $updated_permalink = '';
    $cat_slug = '';
    if ($post->post_type != 'post') {
        return $permalink;
    }

    $taxonomy = 'category'; //Put your custom taxonomy term here
    $terms = wp_get_post_terms($post->ID, $taxonomy);
    // foreach ($terms as $term) {
    //     if ($term->parent == 0) // this gets the parent of the current post taxonomy
    //     {
    //         $parent_term = $term;
    //     }
    // }
    // echo '' . $parent_term->name . '';

    // $cat_slug = $parent_term->name;
    // Right, the parent is set, now let's get the children
    foreach ($terms as $term) {
        if ($term->parent != 0) // this ignores the parent of the current post taxonomy
        {
            $child_term = $term; // this gets the children of the current post taxonomy
            $cat_slug  =  $child_term->name . '/';
        }
    }

    $updated_permalink = str_replace($post->post_name, $cat_slug . $post->post_name, $permalink);

    return $updated_permalink;
}