sub SomeDBRoutine {
  my $self = shift;
  $obj->dbh->WhatEver;
}

sub dbh {
  my $self = shift;
  if ( @_ ) {
    $connection_string = shift;
    $self->{dbh} = DBI->Connect($connection_string, "user","pass");
  }
  return $self->{dbh};
}