graphile/postgraphile

I'm generating error messages for the front end like this:

create or replace function app_public.register_person(
  handle text,
  display_name text,
  email text,
  password text
) returns app_public.person as $$
declare
  person app_public.person;
  constraint_name text;
begin
  insert into app_public.person (handle, display_name) values
    (handle, display_name)
    returning * into person;

  insert into app_private.person_account (person_id, email, password_hash) values
    (person.id, email, crypt(password, gen_salt('bf')));

  return person;

exception 
  when check_violation then
    get stacked diagnostics constraint_name = CONSTRAINT_NAME;
    if constraint_name = 'handle_length' then
      raise exception 'Your handle is too long';
    end if;
  when unique_violation then
    get stacked diagnostics constraint_name = CONSTRAINT_NAME;
    if constraint_name = 'person_account_email_key' then
      raise exception 'That email is already in use';
    elsif constraint_name = 'person_handle_key' then
      raise exception 'That handle is already in use';
    else
      raise exception '%', constraint_name;
    end if;
end;
$$ language plpgsql strict security definer;

It works, but I'm curious as to whether this is the "right" approach or not.