sub new {
  my ($class, @ids) = @_;
  my @users;
  my $sql = "SELECT user_id, user_name FROM users WHERE user_id IN (" . join(",", @ids) . ")";
  my $sth = $dbh->prepare($sql);
  $sth->execute();
  $sth->bind_cols(\my ($id, $name));
  while ( $sth->fetch() ) {
    push @users, bless({
      user_id   => $id,
      user_name => $name,
    }, $class);
  };
  return wantarray ? @users : $users[0];
}