Re: dbi_query_iterator and my misunderstanding the $row

[japhy]

in reply to dbi_query_iterator and my misunderstanding the $row

I think this is because fetchrow_arrayref uses the same location in memory every time, as the DBI docs state: Note that the same array reference is returned for each fetch, so don't store the reference and then use it after a later fetch. Also, the elements of the array are also reused for each row, so take care if you want to take a reference to an element.

[jfroebe]

Thanks! But why return $oldrow->[0] instead of just $row->[0]?

        my $oldrow = $row;
        $row = $sth->fetchrow_arrayref;
        return $oldrow->[0];

[japhy]

Oh, sorry. Maybe I misunderstood. Does the code actually work, and you want to know why it works?

$oldrow is the previous row. The function that builds the iterator stores the first row before it creates the iterator function:

sub dbi_query_iterator {
  my ($sth, @params) = @_;

  $sth->execute(@params) or return;

  # get the first row of results NOW
  my $row = $sth->fetchrow_arrayref();

  return Iterator {
    my $action = shift() || 'nextval';

    if ($action eq 'exhausted?') {
      return ! defined $row;
    } elsif ($action eq 'nextval') {

      # save the current row of results
      my $oldrow = $row;

      # get the next row of results
      $row = $sth->fetchrow_arrayref;

      # return the previous row (before we advanced)
      return $oldrow->[0];
    }
  }
}

[jfroebe]

Thanks! That's what I thought but was confused by the first response. :)