Sort a Perl array of objects by dates

Question

I need to order the @list array by insertDate, but how can I access it since it is a $obj array?

I tried Perl's sort function but I don't understand how it works with this kind of array composed of $obj.

sub getLastQuestions {
  my ($page) = @_;
  $page ||= 1;

  my $questionPerPage = 30;
  my @list            = [];

  my @questions = $db->findNodes("/db/questions/question");

  if (@questions) {
    foreach my $question (@questions) {
      my $id         = $question->findvalue("\@id");
      my $title      = $question->findvalue("title");
      my $author     = $question->findvalue("author");
      my $insertDate = $question->findvalue("insertDate");

      my $obj = Model::Question->new(
        path       => "vedi-domanda.cgi?id=" . $id,
        title      => $title,
        author     => $author,
        insertDate => $insertDate
      );

      # Aggiungi uno
      push @list, $obj;
    }
  }

  return @list;
}

Answer 1

Note that there is no need for

if (@questions) { ... }

because

foreach my $question (@questions) { ... }

will not execute if the array is empty

There is also a bug in your initialisation of @list, which you are setting to []. This doesn't empty the array - it sets it to have one element which contains a reference to an empty array. Just my @list is correct.

The easiest way to do this is to sort the @questions array before transforming it into an array of Model::Question objects.

The exact code depends entirely on the format of the date strings in the XML, but if they are well-formed, like an ISO 8601 date, then they can just be sorted as strings to get the desired effect. So you could write

  my @questions = sort {
    my ($aa, $bb) = map $_->findvalue('insertDate'), ($a, $b);
    $aa cmp $bb;
  } $db->findNodes('/db/questions/question');

Please note that you haven't shown the format of your date strings, so this may not work without some additional coding

You may also want to use map to convert the XML nodes into Model::Question objects, as I show in this subroutine

sub get_last_questions {

  my ($page) = @_;
  $page ||= 1;

  my $_PerPage = 30;

  my @questions = sort {
    my ($aa, $bb) = map $_->findvalue('insertDate'), ($a, $b);
    $aa cmp $bb;
  } $db->findNodes('/db/questions/question');

  my @list = map {
    Model::Question->new(
      path       => 'vedi-domanda.cgi?id=' . $_->findvalue('@id'),
      title      => $_->findvalue('title'),
      author     => $_->findvalue('author'),
      insertDate => $_->findvalue('insertDate'),
    );
  } @questions;

  return @list;
}