How to have multiple relationships to same model when HAS_ONE in both directions with DMZ?

[eluser]godunov[/eluser]
I'm using DataMapper DMZ, trying to make a flashcard here and I have a Card class and a Card_Side class. Each instance of Card_Side has a relationship with exactly one Card, and each instance of Card has exactly one relationship with two different instances of Card_Side, one called front and the other back. SInce these are one-to-one in both directions, I am not using a join table (for the record using a join table doesn't seem to change anything).

My tables (table_name => attributes):

cards => id, front_id, back_id
card_sides => id, card_id

My Relationships:

Card:

Code:

var $has_one = array(
    'front' => array(
        'class' => 'card_side'
    ),
    'back' => array(
        'class' => 'card_side'
    )
);

Card_Side: *I've tried many things here, nothing works for me

Code:

var $has_one = array(
    'card' => array(
        'other_field' => 'back'
    ),
    'card' => array(
        'other_field' => 'front'
    )
);
// Also Tried:
var $has_one = array('card');

Main Script to Create Card and Card_Sides
Here I create a Card, two Card_Sides, and relate them to each other:

Code:

$this->load->model('card', 'card_model');
$this->load->model('card_side', 'side_model');
$empty_card = $this->card_model->create();
if ($empty_card != NULL)
{
    $front = $this->side_model->create();
    $front->save($empty_card);
    
    $back = $this->side_model->create();
    $back->save($empty_card);
    
    echo '$front->id = '.$front->id.'<br>';
    echo '$back->id = '.$back->id.'<br>';
    
    $empty_card->save(
        array(
            'back' => $back,
            'front' => $front
        ));
    
    echo '$empty_card->front->get()->id = '.$empty_card->front->get()->id.'<br>';
    echo '$empty_card->back->get()->id = '.$empty_card->back->get()->id.'<br>';
    echo '$front->card->get()->id = '.$front->card->get()->id.'<br>';
    echo '$back->card->get()->id = '.$back->card->get()->id;
}

Tables After This Code Runs:

cards:
+------+----------+---------+
| id | front_id | back_id |
+------+----------+---------+
| 8239 | 85 | 86 |
+------+----------+---------+

card_sides
+----+---------+
| id | card_id |
+----+---------+
| 85 | NULL |
| 86 | 8239 |
+----+---------+



Here's my problem. Athough the card's "back_id" and "front_id" fields are filled with the correct ids of the two new Card_Sides, the above code doesn't relate the objects together properly. Also the first Card_Side is getting a NULL for its card_id. The echo statements in the code above print the following:

$front->id = 85
$back->id = 86
$empty_card->front->get()->id = 86 :down:
$empty_card->back->get()->id = 86
$front->card->get()->id = 8239
$back->card->get()->id = :down:

So the Card is only associated with the second Card_Side ("back"), and only the first Card_Side ("front") is associated with the Card.

How do I set up my relationships for Card_Sides here? All the examples I've seen of multiple references to the same class have has_many in at least one direction. How do we do has_one in both directions?

Many thanks for any input.