“[something copyWithZone:]: unrecognized selector sent to instance” when using Bindings / Core Data

Question

(self asking and self-answering because I spent hours on the web looking for this, and most of the resources all say \"I solved it in the end\" without giving an explanation

Answer 1

I also had a similar problem and it came from calling a ProxyObject rather than the actual object from an array controller.

For example:

MYEntity *entity = EntityController.selection;
NSString *property = entity.property;   // <--- causes the error

but

MYEntity *entity = EntityController.selectedObjects firstObject]; // <--- fixes the error
NSString *property = entity.property;