[zzzeek]

OK, you're right in that owner_id can refer to a nonexistent entry, if the schema both doesn't make correct use of constraints and is also referentially corrupt. Designing the ORM to jump through huge hoops to suit the case that the user is using the relational database incorrectly, in such a way that enormous performance overhead is added to the use case as used correctly in the vast majority of cases, is IMO a poor design decision.