@Maglok,
Datamapper is about relations, it can’t produce data in a relation that is not related. 😉
The best option is probably to retrieve all hobbies, and retrieve the person including it’s related hobbies. Then iterate over the hobbies, and check if the id exists as a key in persons->hobbies->all. If so, that hobby is related, and if not, well…
That is a good guideline, DM being about relations. Anyway that is how I fixed it indeed. Thanks!