That's just the fat model approach. It suffers from similar issues as fat controllers, whereby unrelated functionality tends to accumulate.

Why do models know how to persist themselves? Or send themselves over the network? What does that have to do with the concept they represent? It conflates technical concerns ("how do I serialize myself?") with business concerns ("am I valid?").

It doesn't help that Core Data forces you into the framework superclass antipattern: http://michaelfeathers.typepad.com/michael_feathers_blog/201...