How to auto increment post title & post slug field?

Question

I've a custom Post Type i.e. prj and need to auto increment it's post_title (title) and post_name (slug) on post save, update regardless of the post status .. the post can never be deleted that's why it won't be an issue ..

Need it to behave just like AutoIncrement field in SQL .. once an ID is assigned, it should never be replicated ..

So far, I've reached to the code mentioned below .. but the problem is it is only setting up the post title, not the slug and the increment feature is not working as well ..

add_filter( 'wp_insert_post_data' , 'odin_prj_title' , '99', 2 );
function odin_prj_title( $data , $postarr )
{
    if( $data['post_type'] == 'prj' ) {
        $last_post = wp_get_recent_posts( '1');
        $last_post_ID = (int)$last_post['0']['ID'];
        $data['post_title'] = 'P0' . ($last_post_ID + 1);
    }
    return $data;
}

Answer 1

I did not work it out using save_post or any other save-filter, so as I am only needing to do the same for the title, I used the default_title filter. This means that it works for drafts as well.

add_filter( 'default_title', 'change_title', 10, 2 );
function change_title( $title, $post ) {
    return 'PO' . $post->ID;
}

Notice that here I am using the newly created post's ID, so I don't have to fetch $last_post_id as you do, and perhaps you don't have to do that either if you do it like this. Remember to check the post type before changing the title though.

I have not tested to do the same with the slug, but I noticed there is a similar filter for the slug, called wp_unique_post_slug. Hopefully this will help you. :)

Edit: here is the filter from WP Core code, https://developer.wordpress.org/reference/functions/wp_unique_post_slug/

Answer 2

I figured out using wp_count_posts function, I can get the last total number of posts and save the title at run-time! Added a bit of conditions as well ..

add_filter( 'wp_insert_post_data' , 'odin_prj_title' , 10, 2 );
function odin_prj_title( $data , $postarr )
{
    if( $data['post_type'] == 'prj' && $data['post_status'] != 'publish' ) {
        $count_posts = wp_count_posts('prj');
        $published_posts = $count_posts->publish;
        $data['post_title'] = 'P0' . ($published_posts + 1);
    }
    return $data;
}