I have created a WordPress site where users register on the front-end and add information about themselves. On registration I am forcing the user_nicename to be name-surname. I am then automatically creating 2 custom post types that act as profile pages for the new users. I am using the user_nicename as the title of both.

The problem is obviously if two people register with the same name.

So I would like to check the database before the user_nicename is updated to check if it already exists. If it does I would like to add an integer (in sequence) to the end of the user_nicename.

For instance:

• John-Smith
• John-Smith-2
• John-Smith-3
• Etc.

The code I have tried is as follows. The exists_in_database piece is clearly where it goes wrong. Any help would be much appreciated. Thank you!

add_action( 'user_registration_after_register_user_action', 'ur_insert_username', 1, 3 );
function ur_insert_username( $valid_form_data, $form_id, $user_id ) {
global $wpdb;

$firstname = isset( $valid_form_data['first_name'] ) ? $valid_form_data['first_name']->value : '';
$lastname = isset( $valid_form_data['last_name'] ) ? $valid_form_data['last_name']->value : '';
$custom_nicename = sanitize_title_with_dashes( $firstname . '-' . $lastname);
    
$i = 1;
do {
  //Check in the database here
  $exists = exists_in_database($custom_nicename);
  if($exists) {
    $i++;
    $name = $first_name . $i;
  }

} while($exists);

$wpdb->update(
    $wpdb->users,
    ['user_nicename' => $custom_nicename],
    ['ID' => $user_id]
    );

{
$user_post_athlete = array(
        'post_title'   => $custom_nicename,
        'post_status'  => 'publish', // <- here is to publish
        'post_type'    => 'athlete', // <- change to your cpt
        'post_author'  => $user_id
    );
    
    $user_post_rivalry = array(
        'post_title'   => $custom_nicename,
        'post_status'  => 'publish', // <- here is to publish
        'post_type'    => 'rivalry', // <- change to your cpt
        'post_author'  => $user_id
    );
    
    // Insert the post into the database
    $post_id = wp_insert_post( $user_post_athlete );
    $post_id = wp_insert_post( $user_post_rivalry );
    }
}