# Create helper
$app->helper(category_select => sub {
  my ($self, $id) = @_;

  my $categories = $self->app->db->resultset('Category');
  
  my $options = Mojo::Collection->new(['*' => 0]);
  while (my $category = $categories->next) {
    my @attr;
    push @attr, selected => 'selected' if $category->id == $id;
    push @{$options}, [$category->name, $category->id, @attr];
  }

  return $options;
});

# _form.html.ep
<td>
  % my $options = category_select $category->id;
  %= select_field parent_id => $options => (class=>'input')
</td>