Under the Hood of Core Data - Core Data - page 10

1.4 NSManagedObject

The NSManagedObject is the object we work with the most in a Core Data appli-
cation. Each instance of the NSManagedObject represents one entity in our Core
Data repository. By combining Core Data with KVO and KVC (discussed in
great detail in Chapter 8, OS X: Bindings, KVC, and KVO , on page 137 ), this
one object can dynamically represent any object that we need and that can
be defined in our data model.

All of the properties and relationships defined in our data model are available
and are easy to access directly from the NSManagedObject . Without subclassing
it, we can access values associated with an NSManagedObject in the following
ways.

Accessing Attributes
Attributes are the easiest to access. By utilizing KVC, we can get or set any
attribute on the NSManagedObject directly. If you have reviewed our sample app
in Appendix 1, Building a Foundation , on page 209 , you may have noticed that
we did not write a Recipe class. At this point in our application, the NSManage-
dObject provides all of the functionality that we require. For example, we could
get the name as follows:

NSManagedObject *recipe = ...;
NSString *name = [recipe valueForKey:@ "name" ];

Likewise, we can set the name in a similar fashion, as follows:

NSManagedObject *recipe = ...;
[recipe setValue:@ "New Name" forKey:@ "name" ];

When we want to subclass NSManagedObject , we can also define properties for
the attributes (and relationships discussed in a moment) so that we can access
them directly. In the header of our subclass, we would define the properties
normally.

RecipesV2/PPRecipes/PPRRecipeMO.h
@interface PPRRecipeMO : NSManagedObject

@property (strong) NSString *desc;
@property (strong) NSString *imagePath;
@property (strong) NSString *lastUsed;
@property (strong) NSString *name;
@property (strong) NSString *serves;
@property (strong) NSString *type;

As you can see, we are defining the property like normal, but there are no
ivars associated with those properties. Since these properties are created