package UserDBConn;
sub new {
  my ($class, $param1, $param2 ...) = @_;
  my $this = bless({}, $class);
  # store the returned DB handle in a private slot
  $this->{_db} = DBI->connect($param1, $param2 ...);
}
sub getDBHandle {
  return $_[0]->{_db};
}

package User;
# lexically scoped at file level so you can create multiple
# instances of this module within this process using the 
# same UserDBConn. Creating a new DB connection each time 
# you want to pull out a user's information would be *bad*.
my $user_db_conn; # = new UserDBConn(...);
sub new {
  my ($class, $username, $more_stuff) = @_;
  my $this = bless({}, $class);
  $user_db_conn ||= new UserDBConn(...);
  # now use $user_db_con->getDBHandle() to populate $this
}
sub setX {}
sub getX {}
sub save {
  # write all our data to the table
}