DataMapper ORM v1.8.0

[eluser]WanWizard[/eluser]
That is not going to work, it is a not supported configuration.

Code:

$u->save($b);

means "save $u, and save the relation between $u and $b". That statement is not aware of anything else. Other fields in the relationship record are considered join fields, and need to be set afterwards.

And if you would save one relation first, and then the second, it would simply generate new records, in which one of the other id's would be NULL.

What you can do is use set_join_field to set the missing id manually:

Code:

$category->save($element->all);
$category->set_join_field($element->all, 'island_id', $island->id);