<?php
use Orm\Model;

class Model_Domain extends \Orm\Model
{

    protected static $_properties = array(
        'id',
        'domain',
        'created_at',
        'updated_at',
    );

    protected static $_many_many = array(
        'users' => array(
            'key_from' => 'id',
            'key_through_from' => 'domain_id',
            'table_through' => 'domains_users',
            'key_through_to' => 'user_id',
            'model_to' => 'Model_User',
            'key_to' => 'id',
            'cascade_save' => true,
            'cascade_delete' => false,
        )
    );

    protected static $_has_many = array(
        'forwards' => array(
            'key_from'            => 'id',
            'model_to'            => 'Model_Forward',
            'key_to'            => 'domain_id',
            'cascade_save'        => true,
            'cascade_delete'    => false
        )
    );

    protected static $_observers = array(
        'Orm\Observer_CreatedAt' => array(
            'events' => array('before_insert'),
            'mysql_timestamp' => false,
        ),
        'Orm\Observer_UpdatedAt' => array(
            'events' => array('before_save'),
            'mysql_timestamp' => false,
        ),
    );

    public static function validate($factory)
    {
        $val = Validation::forge($factory);
        $val->add_field('domain', 'Domain', 'required|max_length[255]');

        return $val;
    }

}

<?php
use Orm\Model;

class Model_User extends \Orm\Model
{
    //protected static $_many_many = array('domains');

    protected static $_many_many = array(
        'domains' => array(
            'key_from' => 'id',
            'key_through_from' => 'domain_id',
            'table_through' => 'domains_users',
            'key_through_to' => 'user_id',
            'model_to' => 'Model_Domain',
            'key_to' => 'id',
            'cascade_save' => true,
            'cascade_delete' => false,
        )
    );

    protected static $_properties = array(
        'id',
        'username',
        'password',
        'group',
        'email',
        'last_login',
        'login_hash',
        'created_at',
        'updated_at',
    );

    protected static $_observers = array(
        'Orm\Observer_CreatedAt' => array(
            'events' => array('before_insert'),
            'mysql_timestamp' => false,
        ),
        'Orm\Observer_UpdatedAt' => array(
            'events' => array('before_save'),
            'mysql_timestamp' => false,
        ),
    );

    public static function validate($factory)
    {
        $val = Validation::forge($factory);
        $val->add_field('username', 'Username', 'required|max_length[50]');
        $val->add_field('password', 'Password', 'required|max_length[255]');
        $val->add_field('group', 'Group', 'required|valid_string[numeric]');
        $val->add_field('email', 'Email', 'required|valid_email|max_length[255]');
        $val->add_field('last_login', 'Last Login', 'required|max_length[25]');
        $val->add_field('login_hash', 'Login Hash', 'required|max_length[255]');

        return $val;
    }

}