what's wrong with dmz library in CI

Question

Hey, i started using the DMZ library and all goes cute expet i’m encoutring a problem : i have three tables :

portals : id - title.. pages : id - portal_id - title.. categories : id - portal_id - title ..

the relation between them is like that : each page and category has one portal . and each portal have many categories and pages . so my models is like that:

//Portal.php
class Portal extends DataMapper {

    var $table = "portals";
    var $has_many = array("category","page");

    function __construct($id = NULL)
    {
        parent::__construct($id);
    }
}

//Page.php
class Page extends DataMapper {

    var $table = "pages";
    var $has_one = array("portal");
    var $has_many = array();

    function __construct($id = NULL)
    {
        parent::__construct($id);
    }
}

//Category.php
class Category extends DataMapper {

    var $table = "categories";
    var $has_one = array("portal");
    var $has_many = array("article");

    function __construct($id = NULL)
    {
        parent::__construct($id);
    }
}  

so in controllers when i use this method :

function cat(){
$category = new category();
        $data['categories'] = $category->get_where(array('portal_id'=>'2'));  

it works fine and return all categories related to portal 2 . when i use this method:

$page = new page();
        $data['portal'] = $page->get_where(array('portal_id'=>'2'));  

the method don’t works fine:

DataMapper Error: ‘page’ is not a valid parent relationship for Portal.

Are your relationships configured correctly? and when i try to get all categories and pages related to portal from the portal i can’t gets them !

$portal = new portal(2);
$categories = $portal->category->get();
$pages = $portal->page->get();//Line 21  

Fatal error: Call to a member function get() on a non-object in G:\AppServ\www\test\application\modules\dir\controllers\home.php on line 21

notice : the line 20 works fine alone it gets all categories related to portal 2 . my database structue :

CREATE TABLE categories ( id int(11) NOT NULL auto_increment,
portal_id int(11) default NULL,
title varchar(255) NOT NULL,
description varchar(600) NOT NULL,
slug varchar(100) NOT NULL,
created datetime NOT NULL,
updated datetime NOT NULL, PRIMARY KEY (id) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=6 ;

CREATE TABLE pages ( id int(11) NOT NULL auto_increment, portal_id int(11) default NULL, title varchar(255) NOT NULL, content longtext NOT NULL, slug varchar(100) NOT NULL, created datetime NOT NULL, updated datetime NOT NULL, PRIMARY KEY (id) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=6 ;

CREATE TABLE portals ( id int(11) NOT NULL auto_increment,
title varchar(150) NOT NULL,
created datetime NOT NULL,
updated datetime NOT NULL, slug varchar(100) NOT NULL, PRIMARY KEY (id), UNIQUE KEY title (title,slug) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=4 ;

so what's wrong?