Orphan polymorphic relations get assigned to random DataObject class about silverstripe-framework

[GuySartorelli]

Expected results: PolyHasOne comes back null

That's not how has_one relations work usually - regular (non-polymorphic) has_one relations give you a singleton of the relevant class. There is a lot of code out there that assumes a dummy record like this will be provided when requesting a non-existent has_one relation so we can't just return null all of a sudden.

i.e. there's a lot of if ($this->MyHasOne()->exists()) {/* do something */} in the wild which would result in exceptions being thrown if we made that change.

[GuySartorelli]

One solution is to always return null for any missing has_one relation in a future major release, which I'd be in favour of.

[maxime-rainville]

I agree that's not clear what the correct outcome should be here. The very confusing thing here is that you'll get a completely random DataObject class on your Polymoprhic has one.

On the related question of what should you get when trying to access an has_one without a value, I think returning null would make more sense. I guess it's a bit better that you are at least getting an instance of the relation's Class.

I'm inclined to call this a CMS6 problem for now.