Validator: A ScheduledSession must be a subEvent of another Event.

[drinkynet]

Might be worth the library throwing a RuntimeException here so that the error can be picked up in development before using the validator.

[nathansalter]

When would you throw the error? The event not having a parent event set is only really an error during serialization, but we don't have enough context in the serializer there to determine easily if the session property is set.

[drinkynet]

It would make sense to do it during serialisation as that is the exact point it should all be valid. Otherwise you'd be wrongly throwing exceptions while building up the model.

I suppose you'd need some pre-serialisation validation method/rule on the model that the serialiser could be aware of to call. But I guess we're into quite a bit of complexity for a little bit of convenience here, and maybe catching it in the validator is fine :)