Swift - Using Core Data With Cocoa - swift

Question

I'm playing with Core Data for an OS X application. The language is Swift. There's something odd about the way it works for Cocoa. The following is a shorter version of what Xcode creates.
class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(aNotification: NSNotification) {
// Insert code here to initialize your application
}
func applicationWillTerminate(aNotification: NSNotification) {
// Insert code here to tear down your application
}
// MARK: - Core Data stack
lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
// The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it. (The directory for the store is created, if necessary.) This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
let fileManager = NSFileManager.defaultManager()
var failError: NSError? = nil
var shouldFail = false
var failureReason = "There was an error creating or loading the application's saved data."
// Make sure the application files directory is there
do {
let properties = try self.applicationDocumentsDirectory.resourceValuesForKeys([NSURLIsDirectoryKey])
if !properties[NSURLIsDirectoryKey]!.boolValue {
failureReason = "Expected a folder to store application data, found a file \(self.applicationDocumentsDirectory.path)."
shouldFail = true
}
} catch {
let nserror = error as NSError
if nserror.code == NSFileReadNoSuchFileError {
do {
try fileManager.createDirectoryAtPath(self.applicationDocumentsDirectory.path!, withIntermediateDirectories: true, attributes: nil)
} catch {
failError = nserror
}
} else {
failError = nserror
}
}
}()
}
And an SQLite file for Core Data is nowhere to be found after I add a new record to an entity. There's no pointer to an SQLite file in the code above. The following is an iOS counterpart.
class AppDelegate: UIResponder, UIApplicationDelegate {
// MARK: - Core Data stack
lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
// The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
// Create the coordinator and store
let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("SingleViewCoreData.sqlite")
var failureReason = "There was an error creating or loading the application's saved data."
do {
try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil)
} catch {
// Report any error we got.
var dict = [String: AnyObject]()
dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
dict[NSLocalizedFailureReasonErrorKey] = failureReason
dict[NSUnderlyingErrorKey] = error as NSError
let wrappedError = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
// Replace this with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog("Unresolved error \(wrappedError), \(wrappedError.userInfo)")
abort()
}
return coordinator
}()
}
The code above points to an SQLite file. So I don't have trouble inserting a record to an entity.
I'm using Xcode 7.2.1 Am I doing something wrong? Or is this an Xcode bug?

Answer 1

The code you have posted here is only part of a functional Core Data stack, and is insufficient to initialise Core Data.
This is Apple's current example code for initialising a Core Data Stack:
import CoreData
class DataController: NSObject {
var managedObjectContext: NSManagedObjectContext
init() {
// This resource is the same name as your xcdatamodeld contained in your project.
guard let modelURL = NSBundle.mainBundle().URLForResource("DataModel", withExtension:"momd") else {
fatalError("Error loading model from bundle")
}
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
guard let mom = NSManagedObjectModel(contentsOfURL: modelURL) else {
fatalError("Error initializing mom from: \(modelURL)")
}
let psc = NSPersistentStoreCoordinator(managedObjectModel: mom)
managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = psc
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {
let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
let docURL = urls[urls.endIndex-1]
/* The directory the application uses to store the Core Data store file.
This code uses a file named "DataModel.sqlite" in the application's documents directory.
*/
let storeURL = docURL.URLByAppendingPathComponent("DataModel.sqlite")
do {
try psc.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: storeURL, options: nil)
} catch {
fatalError("Error migrating store: \(error)")
}
}
}
}
See Initialising the Core Data Stack from Apple.

Answer 2

The Swift 3 version of #DuncanBabbage solution:
class DataController: NSObject {
var managedObjectContext: NSManagedObjectContext
override init() {
// This resource is the same name as your xcdatamodeld contained in your project.
guard let modelURL = Bundle.main.url(forResource: "DataModel", withExtension:"momd") else {
fatalError("Error loading model from bundle")
}
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
guard let mom = NSManagedObjectModel(contentsOf: modelURL) else {
fatalError("Error initializing mom from: \(modelURL)")
}
let psc = NSPersistentStoreCoordinator(managedObjectModel: mom)
managedObjectContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = psc
DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async {
let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
let docURL = urls[urls.endIndex-1]
/* The directory the application uses to store the Core Data store file.
This code uses a file named "DataModel.sqlite" in the application's documents directory.
*/
let storeURL = docURL.appendingPathComponent("DataModel.sqlite")
do {
try psc.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: storeURL, options: nil)
} catch {
fatalError("Error migrating store: \(error)")
}
}
}
}