Make ONLY one URL to a Wordpress post accessible which has child category

Question

Let say a post have parent-category 'Recipes', child-category 'Baking' and post name 'My post title'

Apparently, the post can be accessible via 2 link:

1. https://example.com/recipes/baking/my-post-title/
2. https://example.com/recipes/my-post-title/

I just want the post to be accessible via the first link, not the latter. Is it possible?

Many thanks!

FYI, I used /%category%/%postname%/ as custom structure for permalinks

Answer 1

you can use both post_link hook and a custom rewrite rule.

custom rewrite function:

function post_add_rewrite_rule(){

    $posts = get_posts( array( 'numberposts' => -1) );
    
    if( $posts ){
        foreach($posts as $post ){
            $post_terms = wp_get_object_terms( $post->ID, 'recipes' );
            if( $post_terms ){
                add_rewrite_rule( "^recipes/" . array_pop($post_terms)->slug . "/([^/]+)/?$", 'index.php?post_type=post&name=$matches[1]', 'top' );
            }
        } 
    }
}
add_action('init', 'post_add_rewrite_rule');

post link hook:

function post_custom_permalink( $url, $post, $leavename=false ) {
   
    if ( $post->post_type == 'post' ) {
        $post_terms = wp_get_object_terms( $post->ID, 'recipes' );

        if( !empty($post_terms) ){
            $url =  home_url( '/recipes/' . array_pop($post_terms)->slug . '/' . $post->post_name );
        }
        else{
            $url =  home_url( '/recipes/' . $post->post_name );
        }
    }
  
    return $url;
}
add_filter( 'post_link', 'post_custom_permalink', 10, 3 );

and finally set up your permalink structure to custom structure:

/recipes/%postname%/