sub selection_extend {
  my $self = shift;
  my $result = shift || die "extend needs a resultset to extend\n";
  my $db_lang = new DB::Languages;
  my @languages = @{$db_lang->get()};
  
  foreach my $person (@$result) {
    my @selected_languages = map { $_->{'ID_language'} } 
    @{$self->get_attributes({'id' => $person->{'ID_person'}, 'attribute' => 'has_language_skill',})};
    my @selection_list = map { my $cur_lang = $_->{'ID_language'}; 
    $_->{'selected'} = 'true' if (grep ($_ == $cur_lang, @selected_languages)); 
    $_; } @languages;
    $person->{'has_language_skill'} = \@selection_list;
  }
  return $result;
}