FCO
Create a way for `has-one` relationship use `.create` (created after #472)
The interesting part of it is that it is actually possible set attribute type to the model it is refers to. I.e.: ... Foo.attr.WHICH # MyModel
@vrurg but on that case, Foo.attr should return a Red::Column to make it possible to be used inside .map, .grep, etc...
As @jonathanstowe have said on the original issue, I think returning a model type would be the best way, it could use the .join-on (the same method we use to find joins) to create it with the right external ids... I'll give it a try as soon as possible!
If we do that change, should that generate a new API version?
I don't think it needs a different API version, because Empty is false, a type object is false.
I'm still trying to figure out why... but my change is working if I define the referencing's model as type and does not work if I define it as string:
