Modify custom field input data before creating a new post

Question

I'm try to check input data before it is added to DB. For example:

I have a custom post meta named book_isbn in post page. I want to make sure that this variable $_POST['book_isbn'] is valid before it is added to DB.

So far I know that I can use hook wp_insert_post_data to achieve this. I'm not sure if I did this right. It doesn't work for me. Please check the code below.

add_filter( 'wp_insert_post_data', 'clean_data_before_post_created', '99', 2 );

    function clean_data_before_ad_created( $data , $postarr ) {
          $data['book_isbn'] = clean_isbn($_POST['book_isbn']);
          return $data;
     }

Thank you.

Answer 1

This runs your function right after the post has been saved (created/updated):

add_action('save_post','clean_data_while_saving_post',1);

function clean_data_while_saving_post($post_id) {
  $data = get_post_meta($post_id,'book_isbn',true);
  update_post_meta($post_id,'book_isbn',clean_isbn($data));
}