my $subtext = "sub {\n";
$subtext .= join (" and ",
  map { '$_->get_'.$_.'() eq "'.quotemeta($hashref->{ $_ }).'"' } @keys);
$subtext .= ";\n}";
my $selectsub = eval($subtext);
my @ret = grep(&$selectsub, @{ $self->get_data() });