Learning Core Data for iOS: A Hands-On Guide to Building Core Data Applications

Transformable

The Transformable attribute data type is used to store an Objective-C object. This attribute type is a flexible option that allows you to store an instance of any class. An example of a transformable attribute is an instance of UIColor. When an NSManagedObject subclass is created from an entity containing a transformable attribute, the resulting property type is id. For the id object to make it into the store (and back again), you’ll need to use an instance of NSValueTransformer or an instance of a subclass of NSValueTransformer. This class helps transparently convert the attribute to NSData and back again. This is a reasonably simple process, especially when the class you want to store implements the NSCoding protocol. If it does, ...