The Core Data Stack - Core Data - page 51

Note: Chapter 6, “Versioning and Migration,” covers
NSMigratePersistentStoresAutomaticallyOption . For now, you just need to
know that setting this options tells Core Data to do its best to automatically
merge different versions of a managed object model when the model's entities
or attributes change.
Finally, under the initializer method, add the following method:
func saveContext() {
var error: NSError ? = nil
if context . hasChanges && ! context . save (&error) {
println ( "Could not save: \(error) , \(error?. userInfo ) " )
}
}
This is a convenience method to save the stack's managed object context and
handle any errors that might result.
Switch to ViewController.swift and make the following changes. First, import the
Core Data framework below import UIKit :
import CoreData
Then, add a property inside the class definition to hold the managed object context:
var managedContext: NSManagedObjectContext !
As in the previous chapter, you'll follow the pattern of each view controller having a
reference to the managed object context.
Now open AppDelegate.swift and make the following changes. Again, you need to
import the Core Data framework below import UIKit :
import CoreData
Then, below var window: UIWindow? , add a variable to hold the Core Data stack:
lazy var coreDataStack = CoreDataStack()
You initialize the Core Data stack object as a lazy variable on the application
delegate. This means the stack won't be set up until the first time you access the
property.
Still in AppDelegate.swift , implement
application(_:didFinishLaunchingWithOptions:) as shown below:
func application(application: UIApplication ,