title: How To check if an attribute exists at runtime on a NSManagedObject subclass
body: <p>How to check if an attribute exists for a particular entity at runtime. I will implement a property named dateAddStamp, but not all entities have this attribute. This class will serve as a base for other entity's classes... So I want to check at runtime If I can call  [self setPrimitiveValue:xxx forKey:xxx] or not... 
  Thanks.</p>