In this question, someone asked how to write a validation method for Core Data. I did that, and it looks cool. But one thing doesn't happen: The validation. I can easily set any "bad" value and this method doesn't get called automatically. What's the concept behind this? Must I always first call the validation method before setting any value? So would I write setter methods which call the appropriate validation method first?

And if yes, what's the point of following a strict convention in how to write the validation method signature? I guess there's also some automatic way of validation, then. How to activate this?