PersistentStoreMigrationKit lets perform progressive migrations of Core Data persistent stores easily. It is written in Swift 2.
Persistent stores are migrated progressively according to a migration plan. To devise a migration plan, PersistentStoreMigrationKit requires the metadata from the existing store, the destination managed object model that you'll eventually use to initialize a persistent store coordinator and an array of bundles in which to look for intermediate models. When you have a migration, you are then ready to execute it. If the execution succeeds, the persistent store will be migrated to the latest model you specified.
func configureManagedObjectContextForURL(persistentStoreURL: NSURL) throws -> NSManagedObjectContext {
// These are the required prequisites.
let latestModel: NSManagedObjectModel
let modelBundles: [NSBundle.mainBundle()]
let persistentStoreType = NSSQLiteStoreType
// Load metadata from persistent store.
let persistentStoreMetadata: [String: AnyObject]?
do {
persistentStoreMetadata = try NSPersistentStoreCoordinator.metadataForPersistentStoreOfType(persistentStoreType, URL: persistentStoreURL)
} catch NSCocoaError.FileReadNoSuchFileError {
// The persistent store doesn't exist,
// so no migration is necessary.
persistentStoreMetadata = nil
} catch {
print("Could not retrieve metadata for persistent store at \(persistentStoreURL): \(error)")
throw error
}
// Devise and execute migration plan, if metadata is available,
//
8000
i.e. the persistent store already exists.
if let persistentStoreMetadata = persistentStoreMetadata {
let migrationPlan: MigrationPlan
do {
migrationPlan = try MigrationPlan(storeMetadata: persistentStoreMetadata, destinationModel: latestModel, bundles: modelBundles)
} catch {
print("Could not devise migration plan for persistent store at \(persistentStoreURL): \(error)")
throw error
}
do {
try migrationPlan.executeForStoreAtURL(persistentStoreURL, type: persistentStoreType, destinationURL: persistentStoreURL, storeType: persistentStoreType)
} catch {
print("Could not execute migration plan for persistent store at \(persistentStoreURL): \(error)")
throw error
}
}
// Configure persistent store coordinator and managed object context.
let persistentStoreCoordinator = NSPersistentStoreCoordinator(managedObjectModel: latestModel)
do {
try persistentStoreCoordinator.addPersistentStoreWithType(persistentStoreType, configuration: nil, URL: persistentStoreURL, options: nil)
} catch {
print("Could not load persistent store at \(persistentStoreURL): \(error).")
throw error
}
return NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
}PersistentStoreMigrationKit also comes with the MigrationOperation
class that conveniently wraps the migration plan workflow into an
NSOperation subclass:
func configureManagedObjectContextForURL(persistentStoreURL: NSURL, completionHandler: (NSManagedObjectContext?, error: ErrorType?) -> Void) {
// These are the required prequisites.
let latestModel: NSManagedObjectModel
let modelBundles: [NSBundle.mainBundle()]
let persistentStoreType = NSSQLiteStoreType
let migrationOperation = MigrationOperation()
migrationOperation.sourceURL = persistentStoreURL
migrationOperation.sourceStoreType = persistentStoreType
migrationOperation.destinationURL = persistentStoreURL
migrationOperation.destinationStoreType = persistentStoreType
migrationOperation.destinationModel = latestModel
migrationOperation.bundles = modelBundles
migrationOperation.completionBlock = {
do {
if let error = migrationOperation.error { throw error }
// Configure persistent store coordinator and managed object context.
let persistentStoreCoordinator = NSPersistentStoreCoordinator(managedObjectModel: latestModel)
do {
try persistentStoreCoordinator.addPersistentStoreWithType(persistentStoreType, configuration: nil, URL: persistentStoreURL, options: nil)
} catch {
print("Could not load persistent store at \(persistentStoreURL): \(error).")
throw error
}
completionHandler(NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType), error: nil)
} catch {
completionHandler(nil, error: error)
}
}
operationQueue.addOperation(migrationOperation)
}Both the MigrationPlan and MigrationOperation classes maintain an
NSProgress instance. You can insert it into your own progress tree
when initializing the plan or operation:
let migrationProgress = NSProgress(totalUnitCount: 1)
let migrationPlan: MigrationPlan
do {
migrationProgress.becomeCurrentWithPendingUnitCount(1)
defer { migrationProgress.resignCurrent() }
migrationPlan = try MigrationPlan(storeMetadata: persistentStoreMetadata, destinationModel: latestModel, bundles: modelBundles)
} catch {
// Handle error.
}This project was inspired by and profitted heavily from the article Custom Core Data Migrations by Martin Hwasser and, of course, pretty much everything Marcus S. Zarra has ever said/written about Core Data. Seriously, do yourself a favor and buy his book.
PersistentStoreMigrationKit is released under the MIT License. See the bundled LICENSE file for details.