need help with datamapper orm and nestedsets

[eluser]kev[/eluser]
Hi all,

I just started using datamapper orm, which i found nice. I'm trying to use the nestedsets extenstion that comes with it. I have a categories table with the following field,

id
root_id
left_id
right_id
title

Below is the code im using to test it,

Code:

$tree = new Category();

  $tree->select_root(1);
  $tree->title = 'First Category';
  
  $tree->new_root();
  $tree->get_root();

  $tree->title = 'First Sub Category';

  $tree->new_first_child();

I get this in the table, see below :

id root_id left_id right_id
1 1 1 4
2 1 2 3

have the data been inserted correctly?

I have uploaded an attachment also.

Now that the data is in the database, I tried to ouput it using dump_tree, see code below :

Code:

echo $tree->dump_tree( array('title'), 'html' , FALSE );

But using this I get a blank screen.

This is my model :

Code:

<?php

class Category extends DataMapper {

var $table = 'categories';

    public $nestedsets = array(
        'name' => 'title'
    );
}

Can someome help me understand this?