Datamapper query error. Can't understand what I am doing wrong

[eluser]prestondocks[/eluser]
Hi All,

I am getting the following error when running a query using datamapper

A Database Error Occurred
Error Number: 1054

Unknown column 'category_model_categorys_posts._id' in 'where clause'

SELECT `posts`.* FROM (`posts`) LEFT OUTER JOIN `categorys_posts` category_model_categorys_posts ON `posts`.`id` = `category_model_categorys_posts`.`_id` WHERE `category_model_categorys_posts`.`_id` IS NULL

I have a post_model and a category_model

Here is my category_model

Code:

class Category_model extends DataMapper
{
    var $table = "categorys";
    var $has_many = array('post');
    var $validation = array(
                        'category'=>array(
                            'label'=>'Category',
                            'rules'=>array('required','min_legnth'=>3,'max_legnth'=>50),
                        ),
                        'active'=>array(
                            'label'=>'Active',
                            'rules'=>array('required','valid_match'=>array(1,0)),
                        ),
    );

and here is my post_model and the function that is generating the error

Code:

class Post_model extends DataMapper
{

    var $table = "posts";
    var $has_one = array('user','category');
    var $has_many = array('comment');
    var $validation = array(
                        'title'=>array(
                            'label'=>'Title',
                            'rules'=>array('required','max_legnth'=>120,'min_legnth'=>5),
                        ),
                        'body'=>array(
                            'label'=>'Post Body',
                            'rules'=>array('required','min_legnth'=>5),
                        ),
                        'status'=>array(
                            'label'=>'Post Status',
                            'rules'=>array('required','valid_match'=>array(1,2,3)),
                        ),
    );

function get_by_category($category)
    {
        $c = new Category_model();
        $c->get_where('category',$category);

        $p = new Post_model();
        $p->where_related($c);
        $p->get();
        return $p;
    }

My database has a posts table, categorys table and categorys_posts table.

I am using the tip version of datamapper

Any help much appreciated.

Thanks
Simon