add Post Id before Custom Post Type Slug in WordPress

permalink.php

<?php


// 1. Modify the generated permalink
function custom_post_type_permalink($post_link, $post) {
    if ('download' == $post->post_type) {
        $post_link = home_url(
            user_trailingslashit("downloads/{$post->ID}/{$post->post_name}")
        );
    }
    return $post_link;
}
add_filter('post_type_link', 'custom_post_type_permalink', 10, 2);

// 2. Add rewrite rules to handle the new URL structure
function custom_post_type_rewrite_rules() {
    // Main rewrite rule
    add_rewrite_rule(
        'downloads/([0-9]+)/([^/]+)/?$',
        'index.php?post_type=download&p=$matches[1]',
        'top'
    );
    
    // Pagination support
    add_rewrite_rule(
        'downloads/([0-9]+)/([^/]+)/page/([0-9]{1,})/?$',
        'index.php?post_type=download&p=$matches[1]&paged=$matches[3]',
        'top'
    );
}
add_action('init', 'custom_post_type_rewrite_rules');


function prevent_slug_modification_for_cpt($override_slug, $slug, $post_ID, $post_status, $post_type, $post_parent) {
    // Only apply to our custom post type
    if ('download' === $post_type) {
        // Return the original slug without modification
        return $slug;
    }
    
    // Let WordPress handle other post types normally
    return $override_slug;
}
add_filter('pre_wp_unique_post_slug', 'prevent_slug_modification_for_cpt', 10, 6);