###ResultSet

sub by_problem {
  if(pop eq '') {
    return shift;
  }
  return shift->search(undef, { problem => pop });
}

sub by_page {
  my ($self, $page, $items_per_page) = @_;
  return $self->search(undef, { order_by => { -desc => 'date_submitted' },
    page => $page, rows => $items_per_page });
}

sub by_author {
  if(pop eq '') {
    return shift;
  }
  return shift->search(undef, { author => pop });
}

###Controller

my @submissions = $self->db->resultset('Submission')->by_author(
    $author_filter)->by_problem($problem_filter)->by_page($page,
    $items_per_page);