Core Data - iOS Programming: The Big Nerd Ranch Guide - page 488

One final note on terminology: in the language of entity-relationship modeling, the attrib-
utes and relationships of an entity are collectively known as its properties .
NSManagedObject and subclasses
When an object is fetched with Core Data, its class, by default, is NSManagedObject .
NSManagedObject is a subclass of NSObject that knows how to cooperate with the
rest of Core Data. An NSManagedObject works a bit like a dictionary: it holds a key-
value pair for every property (attribute or relationship) in the entity.
An NSManagedObject is little more than a data container. If you need your model ob-
jects to do something in addition to holding data, you must subclass NSManagedOb-
ject . Then, in your model file, you specify that this entity is represented by instances of
your subclass, not the standard NSManagedObject .
Select the BNRItem entity. Show the data model inspector and change the Class field to
BNRItem , as shown in Figure 16.10 . Now, when a BNRItem entity is fetched with Core
Data, the type of this object will be BNRItem . ( BNRAssetType instances will still be
of type NSManagedObject .)