Example of the new ActiveRecord package

group.php

<?php

namespace Fuel\Application\Model;

use ActiveRecord;

class Group extends ActiveRecord\Model {

	protected $has_many = array('users');

}

user.php

<?php

namespace Fuel\Application\Model;

use ActiveRecord;

class User extends ActiveRecord\Model {

	protected $belongs_to = array('group');

}

welcome.php

<?php

namespace Fuel\Application;

// Not required, just here for nicer syntax
use Fuel\Application\Model\User;
use Fuel\Application\Model\Group;

class Controller_Welcome extends Controller\Base {

	public function action_index()
	{
		// Here I use the 'include' option, which includes the given association by default.
		// Using this allows us to use eager loading to include all the data with 1 query.
		// If you left this out and the query there were 10 rows returned, it would actually
		// run 11 queries, because it would re-query every time you accesses the assoc.

		// Find all the users named 'Dan' and display their ID's and what group they are in
		$users = User::find_by_name('Dan', array('include' => 'group'));

		foreach ($users as $user)
		{
			echo 'ID: '.$user->id.' - Group: '.$user->group->name.'<br />';
		}

		// Same thing as above, just lists all the users in a group
		$group = Group::find(2, array('include' => 'users'));

		foreach($group->users as $user)
		{
			echo $user->name.'<br />';
		}

		// Output the query count.  This will be 2 in this scenario, if we removed
		// the includes it would be N + 2, where N is the number of records returned
		// for each one.
		echo DB::$query_count;
	}

}

Could it be a string if there is only one association?

Yup.

can you add aliases for associations?

protected $has_many = array('menu_items' => 'items');

The reason is that the items model is in a subfolder under menu as it's a property of menu, and that way the tables are called:

menus
menu_items