+1  A: 

Try it like this:

Horseman:
    Hector:
        name: Hector

Stable:
    StableA:
        info: Lorem Ipsum Dolor Sit Amet
        Horseman: Hector

Horses:
    Ed:
        name: Ed
        Horseman: Hector
        Stable: StableA

You don't want to use an id of related object but THE related object. That's why you should use relation names rather than field names.

kuba
Works great in this example, Thanks! But how should that work if i have more than one relation to the same Table? As example: Add a second Horseman to the fixtures and a "id_previous_owner" column to Horses. How to still have Hector be the id_owner and the new Horseman be the id_previous_owner?
FortyTwo
It finally made *bling* .. In the schema within relation you first define a relation name (not giving a table name or something). I had to give every relation a unique name (with the class: option). Thanks again (especially for the last sentence :-))
FortyTwo