added NSProgress support for migrations

CoreStore.xcodeproj/project.pbxproj

@@ -62,6 +62,8 @@
 		B5E84F381AFF85470064E85B /* NSManagedObject+Transaction.swift in Sources */ = {isa = PBXBuildFile; fileRef = B5E84F341AFF85470064E85B /* NSManagedObject+Transaction.swift */; };
 		B5E84F391AFF85470064E85B /* NSManagedObjectContext+Querying.swift in Sources */ = {isa = PBXBuildFile; fileRef = B5E84F351AFF85470064E85B /* NSManagedObjectContext+Querying.swift */; };
 		B5E84F411AFF8CCD0064E85B /* ClauseTypes.swift in Sources */ = {isa = PBXBuildFile; fileRef = B5E84F401AFF8CCD0064E85B /* ClauseTypes.swift */; };
+		B5FAD6A91B50A4B400714891 /* NSProgress+Convenience.swift in Sources */ = {isa = PBXBuildFile; fileRef = B5FAD6A81B50A4B300714891 /* NSProgress+Convenience.swift */; };
+		B5FAD6AC1B51285300714891 /* MigrationManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = B5FAD6AB1B51285300714891 /* MigrationManager.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -158,6 +160,8 @@
 		B5E84F341AFF85470064E85B /* NSManagedObject+Transaction.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSManagedObject+Transaction.swift"; sourceTree = "<group>"; };
 		B5E84F351AFF85470064E85B /* NSManagedObjectContext+Querying.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSManagedObjectContext+Querying.swift"; sourceTree = "<group>"; };
 		B5E84F401AFF8CCD0064E85B /* ClauseTypes.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ClauseTypes.swift; sourceTree = "<group>"; };
+		B5FAD6A81B50A4B300714891 /* NSProgress+Convenience.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSProgress+Convenience.swift"; sourceTree = "<group>"; };
+		B5FAD6AB1B51285300714891 /* MigrationManager.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MigrationManager.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -383,6 +387,7 @@
 			isa = PBXGroup;
 			children = (
 				B5E84F271AFF84920064E85B /* NSManagedObject+Convenience.swift */,
+				B5FAD6A81B50A4B300714891 /* NSProgress+Convenience.swift */,
 			);
 			path = "Convenience Helpers";
 			sourceTree = "<group>";
@@ -391,13 +396,14 @@
 			isa = PBXGroup;
 			children = (
 				B5E84F2A1AFF849C0064E85B /* AssociatedObjects.swift */,
-				B51BE0691B47FC4B0069F532 /* NSManagedObjectModel+Setup.swift */,
 				B5E84F2B1AFF849C0064E85B /* NotificationObserver.swift */,
+				B5FAD6AB1B51285300714891 /* MigrationManager.swift */,
 				B5E84F341AFF85470064E85B /* NSManagedObject+Transaction.swift */,
 				B5E84F2C1AFF849C0064E85B /* NSManagedObjectContext+CoreStore.swift */,
 				B5E84F351AFF85470064E85B /* NSManagedObjectContext+Querying.swift */,
 				B5E84F321AFF85470064E85B /* NSManagedObjectContext+Setup.swift */,
 				B5E84F331AFF85470064E85B /* NSManagedObjectContext+Transaction.swift */,
+				B51BE0691B47FC4B0069F532 /* NSManagedObjectModel+Setup.swift */,
 				B5E84F2D1AFF849C0064E85B /* WeakObject.swift */,
 			);
 			path = Internal;
@@ -558,6 +564,7 @@
 				2F291E2719C6D3CF007AF63F /* CoreStore.swift in Sources */,
 				B5E84F411AFF8CCD0064E85B /* ClauseTypes.swift in Sources */,
 				B5E84F0D1AFF847B0064E85B /* BaseDataTransaction+Querying.swift in Sources */,
+				B5FAD6AC1B51285300714891 /* MigrationManager.swift in Sources */,
 				B5E84EF61AFF846E0064E85B /* DataStack+Transaction.swift in Sources */,
 				B5E84EDF1AFF84500064E85B /* DataStack.swift in Sources */,
 				B5E84F231AFF84860064E85B /* ListMonitor.swift in Sources */,
@@ -566,6 +573,7 @@
 				B5E84EF51AFF846E0064E85B /* BaseDataTransaction.swift in Sources */,
 				B5E84EFB1AFF846E0064E85B /* SaveResult.swift in Sources */,
 				B5E84F0F1AFF847B0064E85B /* From.swift in Sources */,
+				B5FAD6A91B50A4B400714891 /* NSProgress+Convenience.swift in Sources */,
 				B5E84EFC1AFF846E0064E85B /* SynchronousDataTransaction.swift in Sources */,
 				B5E84F281AFF84920064E85B /* NSManagedObject+Convenience.swift in Sources */,
 				B51BE06A1B47FC4B0069F532 /* NSManagedObjectModel+Setup.swift in Sources */,

CoreStore/Convenience Helpers/NSProgress+Convenience.swift

@@ -0,0 +1,112 @@
+//
+//  NSProgress+Convenience.swift
+//  CoreStore
+//
+//  Copyright (c) 2015 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import GCDKit
+
+
+// MARK: - NSProgress
+
+public extension NSProgress {
+    
+    // MARK: Public
+    
+    public func setProgressHandler(closure: ((progress: NSProgress) -> Void)?) {
+        
+        self.progressObserver.progressHandler = closure
+    }
+    
+    
+    // MARK: Private
+    
+    private struct PropertyKeys {
+        
+        static var progressObserver: Void?
+    }
+    
+    private var progressObserver: ProgressObserver {
+        
+        get {
+            
+            let object: AnyObject? = getAssociatedObjectForKey(&PropertyKeys.progressObserver, inObject: self)
+                
+            if let observer = object as? ProgressObserver {
+                
+                return observer
+            }
+            
+            let observer = ProgressObserver(self)
+            setAssociatedRetainedObject(
+                observer,
+                forKey: &PropertyKeys.progressObserver,
+                inObject: self
+            )
+            
+            return observer
+        }
+    }
+}
+
+
+@objc private final class ProgressObserver: NSObject {
+    
+    private weak var progress: NSProgress?
+    private var progressHandler: ((progress: NSProgress) -> Void)?
+    
+    private init(_ progress: NSProgress) {
+        
+        self.progress = progress
+        super.init()
+        
+        progress.addObserver(
+            self,
+            forKeyPath: "fractionCompleted",
+            options: .New,
+            context: nil
+        )
+    }
+    
+    deinit {
+        
+        progress?.removeObserver(self, forKeyPath: "fractionCompleted")
+    }
+    
+    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
+        
+        guard let progress = self.progress where object as? NSProgress == progress && keyPath == "fractionCompleted" else {
+            
+            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
+            return
+        }
+        
+        GCDQueue.Main.async { [weak self] () -> Void in
+            
+            if let strongSelf = self, let progress = strongSelf.progress {
+                
+                strongSelf.progressHandler?(progress: progress)
+            }
+        }
+    }
+}

CoreStore/Internal/MigrationManager.swift

@@ -0,0 +1,61 @@
+//
+//  MigrationManager.swift
+//  CoreStore
+//
+//  Copyright (c) 2015 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import CoreData
+
+
+// MARK: - MigrationManager
+
+internal final class MigrationManager: NSMigrationManager, NSProgressReporting {
+    
+    // MARK: NSObject
+    
+    override func didChangeValueForKey(key: String) {
+        
+        super.didChangeValueForKey(key)
+        
+        if key == "migrationProgress" {
+            
+            let progress = self.progress
+            progress.completedUnitCount = Int64(Float(progress.totalUnitCount) * self.migrationProgress)
+        }
+    }
+    
+    
+    // MARK: NSMigrationManager
+
+    init(sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel, progress: NSProgress) {
+        
+        self.progress = progress
+        
+        super.init(sourceModel: sourceModel, destinationModel: destinationModel)
+    }
+    
+
+    // MARK: NSProgressReporting
+    
+    let progress: NSProgress
+}

CoreStore/Internal/NSManagedObjectContext+Setup.swift

@@ -74,7 +74,8 @@ internal extension NSManagedObjectContext {
         
         let context = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
         context.parentContext = rootContext
-        context.shouldCascadeSavesToParent = true
+        context.mergePolicy = NSRollbackMergePolicy
+        context.shouldCascadeSavesToParent = false
         context.undoManager = nil
         context.setupForCoreStoreWithContextName("com.corestore.maincontext")
         context.observerForDidSaveNotification = NotificationObserver(

CoreStore/Internal/NSManagedObjectModel+Setup.swift

@@ -33,15 +33,65 @@ internal extension NSManagedObjectModel {
     
     // MARK: Internal
     
-    private var modelFileURL: NSURL? {
+    @nonobjc internal class func fromBundle(bundle: NSBundle, modelName: String, modelVersion: String? = nil) -> NSManagedObjectModel {
         
-        get {
+        guard let modelFilePath = bundle.pathForResource(modelName, ofType: "momd") else {
             
-            return self.modelVersionFileURL?.URLByDeletingLastPathComponent
+            fatalError("Could not find \"\(modelName).momd\" from the bundle. \(bundle)")
         }
+        
+        let modelFileURL = NSURL(fileURLWithPath: modelFilePath)
+        let versionInfoPlistURL = modelFileURL.URLByAppendingPathComponent("VersionInfo.plist", isDirectory: false)
+        
+        guard let versionInfo = NSDictionary(contentsOfURL: versionInfoPlistURL),
+            let versionHashes = versionInfo["NSManagedObjectModel_VersionHashes"] as? [String: AnyObject] else {
+                
+                fatalError("Could not load \(typeName(NSManagedObjectModel)) metadata from path \"\(versionInfoPlistURL)\"."
+                )
+        }
+        
+        let modelVersions = Set(versionHashes.keys)
+        let currentModelVersion: String
+        
+        if let modelVersion = modelVersion {
+            
+            currentModelVersion = modelVersion
+        }
+        else {
+            
+            currentModelVersion = versionInfo["NSManagedObjectModel_CurrentVersionName"] as? String ?? modelVersions.first!
+        }
+        
+        var modelVersionFileURL: NSURL?
+        for modelVersion in modelVersions {
+            
+            let fileURL = modelFileURL.URLByAppendingPathComponent("\(modelVersion).mom", isDirectory: false)
+            
+            if modelVersion == currentModelVersion {
+                
+                modelVersionFileURL = fileURL
+                continue
+            }
+            
+            precondition(
+                NSManagedObjectModel(contentsOfURL: fileURL) != nil,
+                "Could not find the \"\(modelVersion).mom\" version file for the model at URL \"\(modelFileURL)\"."
+            )
+        }
+        
+        if let modelVersionFileURL = modelVersionFileURL,
+            let rootModel = NSManagedObjectModel(contentsOfURL: modelVersionFileURL) {
+                
+                rootModel.modelVersionFileURL = modelVersionFileURL
+                rootModel.modelVersions = modelVersions
+                rootModel.currentModelVersion = currentModelVersion
+                return rootModel
+        }
+        
+        fatalError("Could not create an \(typeName(NSManagedObjectModel)) from the model at URL \"\(modelFileURL)\".")
     }
     
-    private(set) var currentModelVersion: String? {
+    @nonobjc private(set) internal var currentModelVersion: String? {
         
         get {
             
@@ -61,7 +111,7 @@ internal extension NSManagedObjectModel {
         }
     }
     
-    private(set) var modelVersions: Set<String>? {
+    @nonobjc private(set) internal var modelVersions: Set<String>? {
         
         get {
             
@@ -81,17 +131,17 @@ internal extension NSManagedObjectModel {
         }
     }
     
-    func entityNameForClass(entityClass: AnyClass) -> String {
+    @nonobjc internal func entityNameForClass(entityClass: AnyClass) -> String {
         
         return self.entityNameMapping[NSStringFromClass(entityClass)]!
     }
     
-    func mergedModels() -> [NSManagedObjectModel] {
+    @nonobjc internal func mergedModels() -> [NSManagedObjectModel] {
         
         return self.modelVersions?.map { self[$0] }.flatMap { $0 == nil ? [] : [$0!] } ?? [self]
     }
     
-    subscript(modelVersion: String) -> NSManagedObjectModel? {
+    @nonobjc internal subscript(modelVersion: String) -> NSManagedObjectModel? {
         
         if modelVersion == self.currentModelVersion {
             
@@ -117,68 +167,32 @@ internal extension NSManagedObjectModel {
         return model
     }
     
-    class func fromBundle(bundle: NSBundle, modelName: String, modelVersion: String? = nil) -> NSManagedObjectModel {
+    @nonobjc internal subscript(metadata: [String: AnyObject]) -> NSManagedObjectModel? {
         
-        guard let modelFilePath = bundle.pathForResource(modelName, ofType: "momd") else {
+        if let modelHashes = metadata[NSStoreModelVersionHashesKey] as? [String : NSData] {
             
-            CoreStore.fatalError("Could not find \"\(modelName).momd\" from the bundle. \(bundle)")
+            for modelVersion in self.modelVersions ?? [] {
-        }
-        
-        let modelFileURL = NSURL(fileURLWithPath: modelFilePath)
-        let versionInfoPlistURL = modelFileURL.URLByAppendingPathComponent("VersionInfo.plist", isDirectory: false)
-        
-        guard let versionInfo = NSDictionary(contentsOfURL: versionInfoPlistURL),
-            let versionHashes = versionInfo["NSManagedObjectModel_VersionHashes"] as? [String: AnyObject] else {
                 
-                CoreStore.fatalError("Could not load \(typeName(NSManagedObjectModel)) metadata from path \"\(versionInfoPlistURL)\"."
+                if let versionModel = self[modelVersion] where modelHashes == versionModel.entityVersionHashesByName {
-                )
+                    
-        }
+                    return versionModel
-        
+                }
-        let modelVersions = Set(versionHashes.keys)
-        let currentModelVersion: String
-        
-        if let modelVersion = modelVersion {
-            
-            precondition(modelVersions.contains(modelVersion))
-            currentModelVersion = modelVersion
-        }
-        else {
-            
-            currentModelVersion = versionInfo["NSManagedObjectModel_CurrentVersionName"] as? String ?? modelVersions.first!
-        }
-        
-        var modelVersionFileURL: NSURL?
-        for modelVersion in modelVersions {
-            
-            let fileURL = modelFileURL.URLByAppendingPathComponent("\(modelVersion).mom", isDirectory: false)
-            
-            if modelVersion == currentModelVersion {
-                
-                modelVersionFileURL = fileURL
-                continue
             }
-            
-            CoreStore.assert(
-                NSManagedObjectModel(contentsOfURL: fileURL) != nil,
-                "Could not find the \"\(modelVersion).mom\" version file for the model at URL \"\(modelFileURL)\"."
-            )
         }
-        
+        return nil
-        if let modelVersionFileURL = modelVersionFileURL,
-            let rootModel = NSManagedObjectModel(contentsOfURL: modelVersionFileURL) {
-                
-                rootModel.modelVersionFileURL = modelVersionFileURL
-                rootModel.modelVersions = modelVersions
-                rootModel.currentModelVersion = currentModelVersion
-                return rootModel
-        }
-        
-        CoreStore.fatalError("Could not create an \(typeName(NSManagedObjectModel)) from the model at URL \"\(modelFileURL)\".")
     }
     
     
     // MARK: Private
     
+    private var modelFileURL: NSURL? {
+        
+        get {
+            
+            return self.modelVersionFileURL?.URLByDeletingLastPathComponent
+        }
+    }
+    
     private var modelVersionFileURL: NSURL? {
         
         get {

CoreStore/Logging/CoreStore+Logging.swift

@@ -46,10 +46,8 @@ public extension CoreStore {
             level: level,
             message: message,
             fileName: fileName,
-            lineNumber:
+            lineNumber: lineNumber,
-            lineNumber,
+            functionName: functionName
-            functionName:
-            functionName
         )
     }
     
@@ -74,14 +72,4 @@ public extension CoreStore {
             functionName: functionName
         )
     }
-    
-    @noreturn internal static func fatalError(message: String, fileName: StaticString = __FILE__, lineNumber: Int = __LINE__, functionName: StaticString = __FUNCTION__) {
-        
-        self.logger.fatalError(
-            message,
-            fileName: fileName,
-            lineNumber: lineNumber,
-            functionName: functionName
-        )
-    }
 }

CoreStore/Logging/CoreStoreLogger.swift

@@ -79,16 +79,6 @@ public protocol CoreStoreLogger {
     :functionName: the source function name
     */
     func assert(@autoclosure condition: () -> Bool, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString)
-    
-    /**
-    Handles fatal errors made throughout the `CoreStore` framework. Implementations should guarantee that the method does not return, either by calling fatalError() or preconditionFailure(), or by raising an exception.
-    
-    :message: the error message
-    :fileName: the source file name
-    :lineNumber: the source line number
-    :functionName: the source function name
-    */
-    @noreturn func fatalError(message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString)
 }
 
 
@@ -96,17 +86,17 @@ public protocol CoreStoreLogger {
 
 internal func typeName<T>(value: T) -> String {
     
-    return "<\(_stdlib_getDemangledTypeName(value))>"
+    return "'\(_stdlib_getDemangledTypeName(value))'"
 }
 
 internal func typeName<T>(value: T.Type) -> String {
     
-    return "<\(value)>"
+    return "'\(value)'"
 }
 
 internal func typeName(value: AnyClass) -> String {
     
-    return "<\(value)>"
+    return "'\(value)'"
 }
 
 internal func typeName(name: String?) -> String {

CoreStore/Logging/DefaultLogger.swift

@@ -42,33 +42,41 @@ public final class DefaultLogger: CoreStoreLogger {
     public func log(level level: LogLevel, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
         
         #if DEBUG
+            let icon: String
             let levelString: String
             switch level {
-            case .Trace: levelString = "Trace"
+                
-            case .Notice: levelString = "Notice"
+            case .Trace:
-            case .Warning: levelString = "Warning"
+                icon = "🔹"
-            case .Fatal: levelString = "Fatal"
+                levelString = "Trace"
+                
+            case .Notice:
+                icon = "🔸"
+                levelString = "Notice"
+                
+            case .Warning:
+                icon = "⚠️"
+                levelString = "Warning"
+                
+            case .Fatal:
+                icon = "❗"
+                levelString = "Fatal"
             }
-            Swift.print("[CoreStore:\(levelString)] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message)\n")
+            Swift.print("\(icon) [CoreStore: \(levelString)] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message)\n")
         #endif
     }
     
     public func handleError(error error: NSError, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
         
         #if DEBUG
-            Swift.print("[CoreStore:Error] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message): \(error)\n")
+            Swift.print("⚠️ [CoreStore: Error] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message): \(error)\n")
         #endif
     }
     
     public func assert(@autoclosure condition: () -> Bool, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
         
         #if DEBUG
-            Swift.assert(condition, message, file: fileName, line: numericCast(lineNumber))
+            Swift.assert(condition, "❗ [CoreStore: Assertion Failure] \(message)", file: fileName, line: numericCast(lineNumber))
         #endif
     }
-    
-    @noreturn public func fatalError(message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
-        
-        Swift.fatalError("[CoreStore:Abort] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message)\n")
-    }
 }

CoreStore/Migrating/DataStack+Migration.swift

@@ -33,16 +33,201 @@ import GCDKit
 public extension DataStack {
     
     /**
-    Checks if the store with the specified filename and configuration needs to be migrated to the `DataStack`'s managed object model version.
+    Asynchronously adds to the stack an SQLite store from the given SQLite file name. Note that using `addSQLiteStore(...)` instead of `addSQLiteStoreAndWait(...)` implies that the migrations are allowed and expected (thus the asynchronous `completion`.)
+    
+    - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory. A new SQLite file will be created if it does not exist. Note that if you have multiple configurations, you will need to specify a different `fileName` explicitly for each of them.
+    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil`, the "Default" configuration. Note that if you have multiple configurations, you will need to specify a different `fileName` explicitly for each of them.
+    - parameter mappingModelBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.allBundles()`.
+    - parameter completion: the closure to be executed on the main queue when the process completes, either due to success or failure. The closure's `PersistentStoreResult` argument indicates the result. If an error is thrown, this closure will not be executed.
+    - returns: an `NSProgress` instance if a migration has started, or `nil` is no migrations are required
+    */
+    public func addSQLiteStore(fileName fileName: String, configuration: String? = nil, mappingModelBundles: [NSBundle]? = nil, completion: (PersistentStoreResult) -> Void) throws -> NSProgress? {
+        
+        return try self.addSQLiteStore(
+            fileURL: applicationSupportDirectory.URLByAppendingPathComponent(
+                fileName,
+                isDirectory: false
+            ),
+            configuration: configuration,
+            mappingModelBundles: mappingModelBundles,
+            completion: completion
+        )
+    }
+    
+    /**
+    Asynchronously adds to the stack an SQLite store from the given SQLite file URL. Note that using `addSQLiteStore(...)` instead of `addSQLiteStoreAndWait(...)` implies that the migrations are allowed and expected (thus the asynchronous `completion`.)
+    
+    - parameter fileURL: the local file URL for the SQLite persistent store. A new SQLite file will be created if it does not exist. If not specified, defaults to a file URL pointing to a "<Application name>.sqlite" file in the "Application Support" directory. Note that if you have multiple configurations, you will need to specify a different `fileURL` explicitly for each of them.
+    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil`, the "Default" configuration. Note that if you have multiple configurations, you will need to specify a different `fileURL` explicitly for each of them.
+    - parameter mappingModelBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.allBundles()`.
+    - parameter completion: the closure to be executed on the main queue when the process completes, either due to success or failure. The closure's `PersistentStoreResult` argument indicates the result.
+    - returns: an `NSProgress` instance if a migration has started, or `nil` is no migrations are required
+    */
+    public func addSQLiteStore(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, mappingModelBundles: [NSBundle]? = NSBundle.allBundles(), completion: (PersistentStoreResult) -> Void) throws -> NSProgress? {
+        
+        CoreStore.assert(
+            fileURL.fileURL,
+            "The specified file URL for the SQLite store is invalid: \"\(fileURL)\""
+        )
+        
+        let coordinator = self.coordinator;
+        if let store = coordinator.persistentStoreForURL(fileURL) {
+            
+            let isExistingStoreAutomigrating = store.options?[NSMigratePersistentStoresAutomaticallyOption] as? Bool == true
+            
+            if store.type == NSSQLiteStoreType
+                && isExistingStoreAutomigrating
+                && store.configurationName == (configuration ?? Into.defaultConfigurationName) {
+                    
+                    GCDQueue.Main.async {
+                        
+                        completion(PersistentStoreResult(store))
+                    }
+                    return nil
+            }
+            
+            let error = NSError(coreStoreErrorCode: .DifferentPersistentStoreExistsAtURL)
+            CoreStore.handleError(
+                error,
+                "Failed to add SQLite \(typeName(NSPersistentStore)) at \"\(fileURL)\" because a different \(typeName(NSPersistentStore)) at that URL already exists."
+            )
+            throw error
+        }
+        
+        do {
+            
+            try NSFileManager.defaultManager().createDirectoryAtURL(
+                fileURL.URLByDeletingLastPathComponent!,
+                withIntermediateDirectories: true,
+                attributes: nil
+            )
+        }
+        catch _ { }
+        
+        do {
+            
+            let metadata = try NSPersistentStoreCoordinator.metadataForPersistentStoreOfType(
+                NSSQLiteStoreType,
+                URL: fileURL
+            )
+            
+            return self.upgradeSQLiteStoreIfNeeded(
+                fileURL: fileURL,
+                metadata: metadata,
+                configuration: configuration,
+                mappingModelBundles: mappingModelBundles,
+                completion: { (result) -> Void in
+                    
+                    if case .Failure(let error) = result {
+                        
+                        completion(PersistentStoreResult(error))
+                        return
+                    }
+                    
+                    let persistentStoreResult = self.addSQLiteStoreAndWait(
+                        fileURL: fileURL,
+                        configuration: configuration,
+                        automigrating: false,
+                        resetStoreOnMigrationFailure: false
+                    )
+                    
+                    completion(persistentStoreResult)
+                }
+            )
+        }
+        catch let error as NSError
+            where error.code == NSFileReadNoSuchFileError && error.domain == NSCocoaErrorDomain {
+                
+                let persistentStoreResult = self.addSQLiteStoreAndWait(
+                    fileURL: fileURL,
+                    configuration: configuration,
+                    automigrating: false,
+                    resetStoreOnMigrationFailure: false
+                )
+                
+                completion(persistentStoreResult)
+                return nil
+        }
+        catch {
+            
+            CoreStore.handleError(
+                error as NSError,
+                "Failed to load SQLite \(typeName(NSPersistentStore)) metadata."
+            )
+            throw error
+        }
+    }
+    
+    /**
+    Migrates an SQLite store with the specified filename to the `DataStack`'s managed object model version WITHOUT adding the migrated store to the data stack.
+    
+    - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory.
+    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil` which indicates the "Default" configuration.
+    - parameter mappingModelBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
+    - parameter sourceBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
+    - returns: an `NSProgress` instance if a migration has started, or `nil` is no migrations are required
+    */
+    public func upgradeSQLiteStoreIfNeeded(fileName fileName: String, configuration: String? = nil, mappingModelBundles: [NSBundle]? = nil, completion: (MigrationResult) -> Void) throws -> NSProgress? {
+        
+        return try self.upgradeSQLiteStoreIfNeeded(
+            fileURL: applicationSupportDirectory.URLByAppendingPathComponent(
+                fileName,
+                isDirectory: false
+            ),
+            configuration: configuration,
+            mappingModelBundles: mappingModelBundles,
+            completion: completion
+        )
+    }
+    
+    /**
+    Migrates an SQLite store at the specified file URL and configuration name to the `DataStack`'s managed object model version. This method does NOT add the migrated store to the data stack.
+    
+    - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory.
+    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil` which indicates the "Default" configuration.
+    - parameter mappingModelBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
+    - parameter sourceBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
+    - returns: an `NSProgress` instance if a migration has started, or `nil` is no migrations are required
+    */
+    public func upgradeSQLiteStoreIfNeeded(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, mappingModelBundles: [NSBundle]? = nil, completion: (MigrationResult) -> Void) throws -> NSProgress? {
+        
+        let metadata: [String: AnyObject]
+        do {
+            
+            metadata = try NSPersistentStoreCoordinator.metadataForPersistentStoreOfType(
+                NSSQLiteStoreType,
+                URL: fileURL
+            )
+        }
+        catch {
+            
+            CoreStore.handleError(
+                error as NSError,
+                "Failed to load SQLite \(typeName(NSPersistentStore)) metadata."
+            )
+            throw error
+        }
+        
+        return self.upgradeSQLiteStoreIfNeeded(
+            fileURL: fileURL,
+            metadata: metadata,
+            configuration: configuration,
+            mappingModelBundles: mappingModelBundles,
+            completion: completion
+        )
+    }
+    
+    /**
+    Checks for the required migrations needed for the store with the specified filename and configuration to be migrated to the `DataStack`'s managed object model version. This method throws an error if the store does not exist, if inspection of the store failed, or no mapping model was found/inferred.
     
     - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory.
     - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil` which indicates the "Default" configuration.
     - parameter mappingModelBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.allBundles()`.
-    :return: a `MigrationType` indicating the type of migration required for the store; or `nil` if either inspection of the store failed, or no mapping model was found/inferred. `MigrationType` acts as a `Bool` and evaluates to `false` if no migration is required, and `true` if either a lightweight or custom migration is needed.
+    :return: an array of `MigrationType`s indicating the chain of migrations required for the store; or `nil` if either inspection of the store failed, or no mapping model was found/inferred. `MigrationType` acts as a `Bool` and evaluates to `false` if no migration is required, and `true` if either a lightweight or custom migration is needed.
     */
-    public func needsMigrationForSQLiteStore(fileName fileName: String, configuration: String? = nil, mappingModelBundles: [NSBundle] = NSBundle.allBundles() as [NSBundle]) -> MigrationType? {
+    public func requiredMigrationsForSQLiteStore(fileName fileName: String, configuration: String? = nil, mappingModelBundles: [NSBundle] = NSBundle.allBundles() as [NSBundle]) throws -> [MigrationType] {
         
-        return needsMigrationForSQLiteStore(
+        return try requiredMigrationsForSQLiteStore(
             fileURL: applicationSupportDirectory.URLByAppendingPathComponent(
                 fileName,
                 isDirectory: false
@@ -60,7 +245,7 @@ public extension DataStack {
     - parameter mappingModelBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.allBundles()`.
     :return: a `MigrationType` indicating the type of migration required for the store; or `nil` if either inspection of the store failed, or no mapping model was found/inferred. `MigrationType` acts as a `Bool` and evaluates to `false` if no migration is required, and `true` if either a lightweight or custom migration is needed.
     */
-    public func needsMigrationForSQLiteStore(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, mappingModelBundles: [NSBundle] = NSBundle.allBundles() as [NSBundle]) -> MigrationType? {
+    public func requiredMigrationsForSQLiteStore(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, mappingModelBundles: [NSBundle] = NSBundle.allBundles() as [NSBundle]) throws -> [MigrationType] {
         
         let metadata: [String : AnyObject]
         do {
@@ -74,101 +259,30 @@ public extension DataStack {
             
             CoreStore.handleError(
                 error as NSError,
-                "Failed to add SQLite \(typeName(NSPersistentStore)) at \"\(fileURL)\"."
+                "Failed to load SQLite \(typeName(NSPersistentStore)) metadata."
             )
-            return nil
+            throw error
         }
         
-        let coordinator = self.coordinator;
+        guard let migrationSteps = self.computeMigrationFromStoreMetadata(metadata, configuration: configuration, mappingModelBundles: mappingModelBundles) else {
-        let destinationModel = coordinator.managedObjectModel
-        if destinationModel.isConfiguration(configuration, compatibleWithStoreMetadata: metadata) {
             
-            return .None
+            let error = NSError(coreStoreErrorCode: .MappingModelNotFound)
-        }
-        
-        guard let sourceModel = NSManagedObjectModel(byMergingModels: [destinationModel], forStoreMetadata: metadata) else {
-            
-            return nil
-        }
-        
-        if let _ = NSMappingModel(
-            fromBundles: mappingModelBundles,
-            forSourceModel: sourceModel,
-            destinationModel: destinationModel) {
-                
-                return .Heavyweight
-        }
-        
-        do {
-            
-            try NSMappingModel.inferredMappingModelForSourceModel(
-                sourceModel,
-                destinationModel: destinationModel
-            )
-            
-            return .Lightweight
-        }
-        catch {
-            
-            return nil
-        }
-    }
-    
-    /**
-    Migrates an SQLite store with the specified filename to the `DataStack`'s managed object model version. This method does NOT add the migrated store to the data stack.
-    
-    - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory.
-    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil` which indicates the "Default" configuration.
-    - parameter sourceBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
-    - parameter sourceBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
-    */
-    public func upgradeSQLiteStoreIfNeeded(fileName fileName: String, configuration: String? = nil, sourceBundles: [NSBundle]? = nil, completion: (MigrationResult) -> Void) -> MigrationType? {
-     
-        return self.upgradeSQLiteStoreIfNeeded(
-            fileURL: applicationSupportDirectory.URLByAppendingPathComponent(
-                fileName,
-                isDirectory: false
-            ),
-            configuration: configuration,
-            sourceBundles: sourceBundles,
-            completion: completion
-        )
-    }
-    
-    /**
-    Migrates an SQLite store at the specified file URL and configuration name to the `DataStack`'s managed object model version. This method does NOT add the migrated store to the data stack.
-    
-    - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory.
-    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil` which indicates the "Default" configuration.
-    - parameter sourceBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
-    - parameter sourceBundles: an optional array of bundles to search mapping model files from. If not set, defaults to the `NSBundle.mainBundle()`.
-    */
-    public func upgradeSQLiteStoreIfNeeded(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, sourceBundles: [NSBundle]? = nil, completion: (MigrationResult) -> Void) -> MigrationType? {
-        
-        let metadata: [String: AnyObject]
-        do {
-            
-            metadata = try NSPersistentStoreCoordinator.metadataForPersistentStoreOfType(
-                NSSQLiteStoreType,
-                URL: fileURL
-            )
-        }
-        catch {
-            
-            let metadataError = error as NSError
             CoreStore.handleError(
-                metadataError,
+                error,
-                "Failed to load SQLite \(typeName(NSPersistentStore)) metadata at \"\(fileURL)\"."
+                "Failed to find migration steps from the store at URL \"\(fileURL)\" to version model \"\(self.modelVersion)\"."
             )
-            
+            throw error
-            GCDQueue.Main.async {
-                
-                completion(MigrationResult(metadataError))
-            }
-            return nil
         }
         
-        guard let migrationSteps = self.computeMigrationFromStoreMetadata(metadata, configuration: configuration, sourceBundles: sourceBundles) else {
+        return migrationSteps.map { $0.migrationType }
+    }
+    
+    
+    // MARK: Private
+    
+    private func upgradeSQLiteStoreIfNeeded(fileURL fileURL: NSURL, metadata: [String: AnyObject], configuration: String?, mappingModelBundles: [NSBundle]?, completion: (MigrationResult) -> Void) -> NSProgress? {
+        
+        guard let migrationSteps = self.computeMigrationFromStoreMetadata(metadata, configuration: configuration, mappingModelBundles: mappingModelBundles) else {
             
             CoreStore.handleError(
                 NSError(coreStoreErrorCode: .MappingModelNotFound),
@@ -182,30 +296,28 @@ public extension DataStack {
             return nil
         }
         
-        if migrationSteps.count == 0 {
+        let numberOfMigrations: Int64 = Int64(migrationSteps.count)
+        if numberOfMigrations == 0 {
             
             GCDQueue.Main.async {
                 
-                completion(MigrationResult(.None))
+                completion(MigrationResult([]))
+                return
             }
-            return .None
+            return nil
         }
         
-        var mergedMigrationType = MigrationType.None
+        let migrationTypes = migrationSteps.map { $0.migrationType }
         var migrationResult: MigrationResult?
-        
         var operations = [NSOperation]()
         var cancelled = false
-        for (sourceModel, destinationModel, mappingModel, migrationType) in migrationSteps {
+        
+        let progress = NSProgress(totalUnitCount: numberOfMigrations)
+        
+        for (sourceModel, destinationModel, mappingModel, _) in migrationSteps {
             
-            switch (mergedMigrationType, migrationType) {
+            progress.becomeCurrentWithPendingUnitCount(1)
-                
+            let childProgress = NSProgress(totalUnitCount: 100)
-            case (.None, _), (.Lightweight, .Heavyweight):
-                mergedMigrationType = migrationType
-                
-            default:
-                break
-            }
             
             operations.append(
                 NSBlockOperation { [weak self] in
@@ -223,8 +335,10 @@ public extension DataStack {
                                 fileURL: fileURL,
                                 sourceModel: sourceModel,
                                 destinationModel: destinationModel,
-                                mappingModel: mappingModel
+                                mappingModel: mappingModel,
+                                progress: childProgress
                             )
+                            childProgress.setProgressHandler(nil)
                         }
                         catch {
                             
@@ -232,8 +346,16 @@ public extension DataStack {
                             cancelled = true
                         }
                     }
+                    
+                    GCDQueue.Main.async {
+                        
+                        withExtendedLifetime(childProgress) { (_: NSProgress) -> Void in }
+                        return
+                    }
                 }
             )
+            
+            progress.resignCurrent()
         }
         
         let migrationOperation = NSBlockOperation()
@@ -243,7 +365,9 @@ public extension DataStack {
             
             GCDQueue.Main.async {
                 
-                completion(migrationResult ?? MigrationResult(mergedMigrationType))
+                completion(migrationResult ?? MigrationResult(migrationTypes))
+                
+                withExtendedLifetime(progress) { (_: NSProgress) -> Void in }
                 return
             }
         }
@@ -252,105 +376,10 @@ public extension DataStack {
         
         self.migrationQueue.addOperations(operations, waitUntilFinished: false)
         
-        return mergedMigrationType
+        return progress
     }
     
-    /**
+    private func computeMigrationFromStoreMetadata(metadata: [String: AnyObject], configuration: String? = nil, mappingModelBundles: [NSBundle]? = nil) -> [(sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel, mappingModel: NSMappingModel, migrationType: MigrationType)]? {
-    Asynchronously adds to the stack an SQLite store from the given SQLite file name. Note that using `addSQLiteStore(...)` instead of `addSQLiteStoreAndWait(...)` implies that the migrations are allowed and expected (thus the asynchronous `completion`.)
-    
-    - parameter fileName: the local filename for the SQLite persistent store in the "Application Support" directory. A new SQLite file will be created if it does not exist. Note that if you have multiple configurations, you will need to specify a different `fileName` explicitly for each of them.
-    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil`, the "Default" configuration. Note that if you have multiple configurations, you will need to specify a different `fileName` explicitly for each of them.
-    - parameter completion: the closure to be executed on the main queue when the process completes, either due to success or failure. The closure's `PersistentStoreResult` argument indicates the result.
-    */
-    public func addSQLiteStore(fileName fileName: String, configuration: String? = nil, sourceBundles: [NSBundle]? = nil, completion: (PersistentStoreResult) -> Void) {
-        
-        self.addSQLiteStore(
-            fileURL: applicationSupportDirectory.URLByAppendingPathComponent(
-                fileName,
-                isDirectory: false
-            ),
-            configuration: configuration,
-            sourceBundles: sourceBundles,
-            completion: completion
-        )
-    }
-    
-    /**
-    Asynchronously adds to the stack an SQLite store from the given SQLite file URL. Note that using `addSQLiteStore(...)` instead of `addSQLiteStoreAndWait(...)` implies that the migrations are allowed and expected (thus the asynchronous `completion`.)
-    
-    - parameter fileURL: the local file URL for the SQLite persistent store. A new SQLite file will be created if it does not exist. If not specified, defaults to a file URL pointing to a "<Application name>.sqlite" file in the "Application Support" directory. Note that if you have multiple configurations, you will need to specify a different `fileURL` explicitly for each of them.
-    - parameter configuration: an optional configuration name from the model file. If not specified, defaults to `nil`, the "Default" configuration. Note that if you have multiple configurations, you will need to specify a different `fileURL` explicitly for each of them.
-    - parameter completion: the closure to be executed on the main queue when the process completes, either due to success or failure. The closure's `PersistentStoreResult` argument indicates the result.
-    */
-    public func addSQLiteStore(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, sourceBundles: [NSBundle]? = NSBundle.allBundles(), completion: (PersistentStoreResult) -> Void) {
-        
-        let coordinator = self.coordinator;
-        if let store = coordinator.persistentStoreForURL(fileURL) {
-            
-            let isExistingStoreAutomigrating = store.options?[NSMigratePersistentStoresAutomaticallyOption] as? Bool == true
-            
-            if store.type == NSSQLiteStoreType
-                && isExistingStoreAutomigrating
-                && store.configurationName == (configuration ?? Into.defaultConfigurationName) {
-                    
-                    GCDQueue.Main.async {
-                        
-                        completion(PersistentStoreResult(store))
-                    }
-                    return
-            }
-            
-            CoreStore.handleError(
-                NSError(coreStoreErrorCode: .DifferentPersistentStoreExistsAtURL),
-                "Failed to add SQLite \(typeName(NSPersistentStore)) at \"\(fileURL)\" because a different \(typeName(NSPersistentStore)) at that URL already exists."
-            )
-            
-            GCDQueue.Main.async {
-                
-                completion(PersistentStoreResult(.DifferentPersistentStoreExistsAtURL))
-            }
-            return
-        }
-        
-        do {
-            
-            try NSFileManager.defaultManager().createDirectoryAtURL(
-                fileURL.URLByDeletingLastPathComponent!,
-                withIntermediateDirectories: true,
-                attributes: nil
-            )
-        }
-        catch _ { }
-        
-        self.upgradeSQLiteStoreIfNeeded(
-            fileURL: fileURL,
-            configuration: configuration,
-            sourceBundles: sourceBundles,
-            completion: { (result) -> Void in
-                
-                if case .Failure(let error) = result
-                    where error.domain != NSCocoaErrorDomain || error.code != NSFileReadNoSuchFileError {
-                        
-                        completion(PersistentStoreResult(error))
-                        return
-                }
-                
-                let persistentStoreResult = self.addSQLiteStoreAndWait(
-                    fileURL: fileURL,
-                    configuration: configuration,
-                    automigrating: false,
-                    resetStoreOnMigrationFailure: false
-                )
-                
-                completion(persistentStoreResult)
-            }
-        )
-    }
-    
-    
-    // MARK: Private
-    
-    private func computeMigrationFromStoreMetadata(metadata: [String: AnyObject], configuration: String? = nil, sourceBundles: [NSBundle]? = nil) -> [(sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel, mappingModel: NSMappingModel, migrationType: MigrationType)]? {
         
         let model = self.model
         if model.isConfiguration(configuration, compatibleWithStoreMetadata: metadata) {
@@ -358,42 +387,16 @@ public extension DataStack {
             return []
         }
         
-        let metadataModel = NSManagedObjectModel(byMergingModels: model.mergedModels(), forStoreMetadata: metadata)!
+        guard let initialModel = model[metadata],
-        if let bypassModel = NSMappingModel(
+            var currentVersion = initialModel.currentModelVersion else {
-            fromBundles: sourceBundles,
-            forSourceModel: metadataModel,
-            destinationModel: model) {
                 
-                return [
+                return nil
-                    (
-                        sourceModel: metadataModel,
-                        destinationModel: model,
-                        mappingModel: bypassModel,
-                        migrationType: .Heavyweight
-                    )
-                ]
         }
         
-        var initialModel: NSManagedObjectModel?
+        let migrationChain: MigrationChain = self.migrationChain.empty
-        if let modelHashes = metadata[NSStoreModelVersionHashesKey] as? [String : NSData],
+            ? [currentVersion: model.currentModelVersion!]
-            let modelVersions = model.modelVersions {
+            : self.migrationChain
-                
-                for modelVersion in modelVersions {
-                    
-                    if let versionModel = model[modelVersion] where modelHashes == versionModel.entityVersionHashesByName {
-                        
-                        initialModel = versionModel
-                        break
-                    }
-                }
-        }
         
-        guard var currentVersion = initialModel?.currentModelVersion else {
-            
-            return nil
-        }
-        
-        let migrationChain = self.migrationChain
         var migrationSteps = [(sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel, mappingModel: NSMappingModel, migrationType: MigrationType)]()
         
         while let nextVersion = migrationChain.nextVersionFrom(currentVersion),
@@ -401,7 +404,7 @@ public extension DataStack {
             let destinationModel = model[nextVersion] {
                 
                 if let mappingModel = NSMappingModel(
-                    fromBundles: sourceBundles,
+                    fromBundles: mappingModelBundles,
                     forSourceModel: sourceModel,
                     destinationModel: destinationModel) {
                         
@@ -410,7 +413,10 @@ public extension DataStack {
                                 sourceModel: sourceModel,
                                 destinationModel: destinationModel,
                                 mappingModel: mappingModel,
-                                migrationType: .Heavyweight
+                                migrationType: .Heavyweight(
+                                    sourceVersion: currentVersion,
+                                    destinationVersion: nextVersion
+                                )
                             )
                         )
                 }
@@ -428,7 +434,10 @@ public extension DataStack {
                                 sourceModel: sourceModel,
                                 destinationModel: destinationModel,
                                 mappingModel: mappingModel,
-                                migrationType: .Lightweight
+                                migrationType: .Lightweight(
+                                    sourceVersion: currentVersion,
+                                    destinationVersion: nextVersion
+                                )
                             )
                         )
                     }
@@ -448,7 +457,7 @@ public extension DataStack {
         return nil
     }
     
-    private func startMigrationForSQLiteStore(fileURL fileURL: NSURL, sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel, mappingModel: NSMappingModel) throws {
+    private func startMigrationForSQLiteStore(fileURL fileURL: NSURL, sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel, mappingModel: NSMappingModel, progress: NSProgress) throws {
         
         autoreleasepool {
             
@@ -462,25 +471,10 @@ public extension DataStack {
             try! journalUpdatingCoordinator.removePersistentStore(store)
         }
         
-        let migrationManager = NSMigrationManager(
+        let migrationManager = MigrationManager(
             sourceModel: sourceModel,
-            destinationModel: destinationModel
+            destinationModel: destinationModel,
-        )
+            progress: progress
-        
-        var lastReportedProgress: Float = -1
-        let timer = GCDTimer.createSuspended(
-            .Main,
-            interval: 0.1,
-            eventHandler: { (timer) -> Void in
-                
-                let progress = migrationManager.migrationProgress
-                if progress > lastReportedProgress {
-                    
-                    // TODO: progress
-                    CoreStore.log(.Trace, message: "migration progress: \(progress)")
-                    lastReportedProgress = progress
-                }
-            }
         )
         
         let temporaryDirectoryURL = NSURL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true).URLByAppendingPathComponent(NSProcessInfo().globallyUniqueString)
@@ -493,6 +487,7 @@ public extension DataStack {
         )
         
         let temporaryFileURL = temporaryDirectoryURL.URLByAppendingPathComponent(fileURL.lastPathComponent!, isDirectory: false)
+        
         do {
             
             try migrationManager.migrateStoreFromURL(
@@ -507,25 +502,22 @@ public extension DataStack {
         }
         catch {
             
-            timer.suspend()
-            
             do {
                 
                 try fileManager.removeItemAtURL(temporaryDirectoryURL)
             }
             catch _ { }
             
-            let migrationError = error as NSError
+            let sourceVersion = migrationManager.sourceModel.currentModelVersion ?? "???"
+            let destinationVersion = migrationManager.destinationModel.currentModelVersion ?? "???"
             CoreStore.handleError(
-                migrationError,
+                error as NSError,
-                "Failed to migrate from version model \"\(migrationManager.sourceModel)\" to version model \"\(migrationManager.destinationModel)\"."
+                "Failed to migrate from version model \"\(sourceVersion)\" to version model \"\(destinationVersion)\"."
             )
             
             throw error
         }
         
-        timer.suspend()
-        
         do {
             
             try fileManager.replaceItemAtURL(
@@ -536,6 +528,8 @@ public extension DataStack {
                 resultingItemURL: nil
             )
             
+            progress.completedUnitCount = progress.totalUnitCount
+            
             do {
                 
                 try fileManager.removeItemAtPath(fileURL.path! + "-shm")
@@ -550,10 +544,11 @@ public extension DataStack {
             }
             catch _ { }
             
-            let replaceError = error as NSError
+            let sourceVersion = migrationManager.sourceModel.currentModelVersion ?? "???"
+            let destinationVersion = migrationManager.destinationModel.currentModelVersion ?? "???"
             CoreStore.handleError(
-                replaceError,
+                error as NSError,
-                "Failed to save store after migrating from version model \"\(migrationManager.sourceModel)\" to version model \"\(migrationManager.destinationModel)\"."
+                "Failed to save store after migrating from version model \"\(sourceVersion)\" to version model \"\(destinationVersion)\"."
             )
             
             throw error

CoreStore/Migrating/MigrationChain.swift

@@ -137,6 +137,11 @@ public struct MigrationChain: NilLiteralConvertible, StringLiteralConvertible, D
     internal let leafVersions: Set<String>
     internal let valid: Bool
     
+    internal var empty: Bool {
+        
+        return self.versionTree.count <= 0
+    }
+    
     internal func contains(version: String) -> Bool {
         
         return self.rootVersions.contains(version)

CoreStore/Migrating/MigrationResult.swift

@@ -38,17 +38,53 @@ public enum MigrationType: BooleanType {
     /**
     Indicates that the persistent store matches the latest model version and no migration is needed
     */
-    case None
+    case None(version: String)
     
     /**
     Indicates that the persistent store does not match the latest model version but Core Data can infer the mapping model, so a lightweight migration is needed
     */
-    case Lightweight
+    case Lightweight(sourceVersion: String, destinationVersion: String)
     
     /**
     Indicates that the persistent store does not match the latest model version and Core Data could not infer a mapping model, so a custom migration is needed
     */
-    case Heavyweight
+    case Heavyweight(sourceVersion: String, destinationVersion: String)
+    
+    /**
+    Returns the source model version for the migration type. If no migration is required, `sourceVersion` will be equal to the `destinationVersion`.
+    */
+    public var sourceVersion: String {
+        
+        switch self {
+            
+        case .None(let version):
+            return version
+            
+        case .Lightweight(let sourceVersion, _):
+            return sourceVersion
+            
+        case .Heavyweight(let sourceVersion, _):
+            return sourceVersion
+        }
+    }
+    
+    /**
+    Returns the destination model version for the migration type. If no migration is required, `destinationVersion` will be equal to the `sourceVersion`.
+    */
+    public var destinationVersion: String {
+        
+        switch self {
+            
+        case .None(let version):
+            return version
+            
+        case .Lightweight(_, let destinationVersion):
+            return destinationVersion
+            
+        case .Heavyweight(_, let destinationVersion):
+            return destinationVersion
+        }
+    }
     
     
     // MARK: BooleanType
@@ -103,7 +139,7 @@ public enum MigrationResult {
     /**
     `MigrationResult.Success` indicates that the `commit()` for the transaction succeeded, either because the save succeeded or because there were no changes to save. The associated value `hasChanges` indicates if there were saved changes or not.
     */
-    case Success(MigrationType)
+    case Success([MigrationType])
     
     /**
     `SaveResult.Failure` indicates that the `commit()` for the transaction failed. The associated object for this value is the related `NSError` instance.
@@ -113,9 +149,9 @@ public enum MigrationResult {
     
     // MARK: Internal
     
-    internal init(_ migrationType: MigrationType) {
+    internal init(_ migrationTypes: [MigrationType]) {
         
-        self = .Success(migrationType)
+        self = .Success(migrationTypes)
     }
     
     internal init(_ error: NSError) {

CoreStore/Saving and Processing/BaseDataTransaction.swift

@@ -70,10 +70,10 @@ public /*abstract*/ class BaseDataTransaction {
                 return object
                 
             case (.None, true):
-                CoreStore.fatalError("Attempted to create an entity of type \(typeName(entityClass)) with ambiguous destination persistent store, but the configuration name was not specified.")
+                fatalError("Attempted to create an entity of type \(typeName(entityClass)) with ambiguous destination persistent store, but the configuration name was not specified.")
                 
             default:
-                CoreStore.fatalError("Attempted to create an entity of type \(typeName(entityClass)), but a destination persistent store containing the entity type could not be found.")
+                fatalError("Attempted to create an entity of type \(typeName(entityClass)), but a destination persistent store containing the entity type could not be found.")
             }
         }
         else {
@@ -88,11 +88,11 @@ public /*abstract*/ class BaseDataTransaction {
             default:
                 if let configuration = into.configuration {
                     
-                    CoreStore.fatalError("Attempted to create an entity of type \(typeName(entityClass)) into the configuration \"\(configuration)\", which it doesn't belong to.")
+                    fatalError("Attempted to create an entity of type \(typeName(entityClass)) into the configuration \"\(configuration)\", which it doesn't belong to.")
                 }
                 else {
                     
-                    CoreStore.fatalError("Attempted to create an entity of type \(typeName(entityClass)) into the default configuration, which it doesn't belong to.")
+                    fatalError("Attempted to create an entity of type \(typeName(entityClass)) into the default configuration, which it doesn't belong to.")
                 }
             }
         }

CoreStore/Setting Up/DataStack.swift

@@ -47,7 +47,7 @@ public final class DataStack {
     /**
     Initializes a `DataStack` from an `NSManagedObjectModel`.
     
-    - parameter modelName: the name of the (.xcdatamodeld) model file. If not specified, the application name will be used
+    - parameter modelName: the name of the (.xcdatamodeld) model file. If not specified, the application name will be used.
     - parameter bundle: an optional bundle to load models from. If not specified, the main bundle will be used.
     - parameter migrationChain: the `MigrationChain` that indicates the heirarchy of the model's version names. If not specified, will default to a non-migrating data stack.
     */
@@ -74,6 +74,14 @@ public final class DataStack {
         self.rootSavingContext.parentStack = self
     }
     
+    /**
+    Returns the `DataStack`'s model version. The version string is the same as the name of the .xcdatamodeld file.
+    */
+    public var modelVersion: String {
+        
+        return self.model.currentModelVersion!
+    }
+    
     /**
     Adds an in-memory store to the stack.
     
@@ -160,6 +168,11 @@ public final class DataStack {
     */
     public func addSQLiteStoreAndWait(fileURL fileURL: NSURL = defaultSQLiteStoreURL, configuration: String? = nil, automigrating: Bool = true, resetStoreOnMigrationFailure: Bool = false) -> PersistentStoreResult {
         
+        CoreStore.assert(
+            fileURL.fileURL,
+            "The specified file URL for the SQLite store is invalid: \"\(fileURL)\""
+        )
+        
         let coordinator = self.coordinator;
         if let store = coordinator.persistentStoreForURL(fileURL) {
             

CoreStoreDemo/CoreStoreDemo/Base.lproj/Main.storyboard

@@ -136,31 +136,54 @@
                             <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>
                             <subviews>
                                 <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="Organism" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="C06-r4-27K">
-                                    <rect key="frame" x="20" y="20" width="560" height="26.5"/>
+                                    <rect key="frame" x="20" y="90" width="560" height="26.5"/>
                                     <fontDescription key="fontDescription" name="HelveticaNeue-Bold" family="Helvetica Neue" pointSize="22"/>
                                     <color key="textColor" red="0.92549019610000005" green="0.94117647059999998" blue="0.94509803920000002" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                                     <nil key="highlightedColor"/>
                                 </label>
                                 <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="attributes" lineBreakMode="wordWrap" numberOfLines="0" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="fXh-OL-4Qb">
-                                    <rect key="frame" x="20" y="70" width="560" height="20.5"/>
+                                    <rect key="frame" x="20" y="140" width="560" height="20.5"/>
                                     <fontDescription key="fontDescription" name="HelveticaNeue-Light" family="Helvetica Neue" pointSize="17"/>
                                     <color key="textColor" red="0.92549019610000005" green="0.94117647059999998" blue="0.94509803920000002" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                                     <nil key="highlightedColor"/>
                                 </label>
+                                <segmentedControl opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="left" contentVerticalAlignment="top" segmentControlStyle="plain" selectedSegmentIndex="0" translatesAutoresizingMaskIntoConstraints="NO" id="Hwa-fO-fC5">
+                                    <rect key="frame" x="20" y="20" width="560" height="29"/>
+                                    <segments>
+                                        <segment title="First"/>
+                                        <segment title="Second"/>
+                                        <segment title=""/>
+                                    </segments>
+                                    <color key="tintColor" cocoaTouchSystemColor="tableCellGroupedBackgroundColor"/>
+                                    <connections>
+                                        <action selector="segmentedControlValueChanged:" destination="hJK-5I-1TQ" eventType="valueChanged" id="jNH-gx-mOg"/>
+                                    </connections>
+                                </segmentedControl>
+                                <progressView opaque="NO" contentMode="scaleToFill" verticalHuggingPriority="750" progress="0.5" translatesAutoresizingMaskIntoConstraints="NO" id="H1P-2g-DHX">
+                                    <rect key="frame" x="20" y="68" width="560" height="2"/>
+                                    <color key="progressTintColor" red="1" green="1" blue="1" alpha="1" colorSpace="calibratedRGB"/>
+                                    <color key="trackTintColor" white="1" alpha="0.20000000000000001" colorSpace="calibratedWhite"/>
+                                </progressView>
                             </subviews>
                             <color key="backgroundColor" red="0.20392156859999999" green="0.28627450980000002" blue="0.36862745099999999" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                             <constraints>
+                                <constraint firstItem="H1P-2g-DHX" firstAttribute="leading" secondItem="5Hd-jr-1nW" secondAttribute="leading" constant="20" id="2Nf-U0-bTq"/>
                                 <constraint firstItem="fXh-OL-4Qb" firstAttribute="top" secondItem="C06-r4-27K" secondAttribute="bottom" constant="23.5" id="6d1-A5-Zc5"/>
-                                <constraint firstAttribute="trailing" secondItem="C06-r4-27K" secondAttribute="trailing" constant="20" id="DC3-u7-f9M"/>
+                                <constraint firstItem="Hwa-fO-fC5" firstAttribute="leading" secondItem="5Hd-jr-1nW" secondAttribute="leading" constant="20" id="CDZ-qV-3eK"/>
+                                <constraint firstItem="H1P-2g-DHX" firstAttribute="top" secondItem="Hwa-fO-fC5" secondAttribute="bottom" constant="20" id="Dcs-Vv-Xfv"/>
                                 <constraint firstItem="fXh-OL-4Qb" firstAttribute="leading" secondItem="C06-r4-27K" secondAttribute="leading" id="SnQ-Ra-KkU"/>
-                                <constraint firstItem="C06-r4-27K" firstAttribute="top" secondItem="5Hd-jr-1nW" secondAttribute="top" constant="20" id="abW-Z0-uln"/>
+                                <constraint firstItem="Hwa-fO-fC5" firstAttribute="top" secondItem="5Hd-jr-1nW" secondAttribute="top" constant="20" id="Zo1-kW-kAw"/>
+                                <constraint firstItem="C06-r4-27K" firstAttribute="top" secondItem="H1P-2g-DHX" secondAttribute="bottom" constant="20" id="bBW-Bn-oeN"/>
                                 <constraint firstAttribute="trailing" secondItem="fXh-OL-4Qb" secondAttribute="trailing" constant="20" id="mhR-0c-i0n"/>
                                 <constraint firstAttribute="trailing" secondItem="C06-r4-27K" secondAttribute="trailing" constant="20" id="s0c-XG-e70"/>
+                                <constraint firstAttribute="trailing" secondItem="H1P-2g-DHX" secondAttribute="trailing" constant="20" id="swp-18-f5e"/>
+                                <constraint firstItem="C06-r4-27K" firstAttribute="top" secondItem="Hwa-fO-fC5" secondAttribute="bottom" constant="20" id="tYt-wb-Lk8"/>
+                                <constraint firstAttribute="trailing" secondItem="Hwa-fO-fC5" secondAttribute="trailing" constant="20" id="ujX-gH-Wlm"/>
                                 <constraint firstItem="C06-r4-27K" firstAttribute="leading" secondItem="5Hd-jr-1nW" secondAttribute="leading" constant="20" id="yiG-c9-BZg"/>
                             </constraints>
                             <variation key="default">
                                 <mask key="constraints">
-                                    <exclude reference="DC3-u7-f9M"/>
+                                    <exclude reference="tYt-wb-Lk8"/>
                                 </mask>
                             </variation>
                         </view>
@@ -206,6 +229,8 @@
                     <simulatedToolbarMetrics key="simulatedBottomBarMetrics"/>
                     <connections>
                         <outlet property="organismLabel" destination="fXh-OL-4Qb" id="shX-fK-haw"/>
+                        <outlet property="progressView" destination="H1P-2g-DHX" id="Asy-fE-gXI"/>
+                        <outlet property="segmentedControl" destination="Hwa-fO-fC5" id="myL-tO-4ah"/>
                         <outlet property="titleLabel" destination="C06-r4-27K" id="zQr-YC-moe"/>
                     </connections>
                 </tableViewController>

CoreStoreDemo/CoreStoreDemo/MIgrations Demo/MigrationsDemoViewController.swift

@@ -19,7 +19,39 @@ class MigrationsDemoViewController: UITableViewController {
     override func viewDidLoad() {
         
         super.viewDidLoad()
-        self.selectModelVersion(self.models.first!)
+        
+        let models = self.models
+        if let segmentedControl = self.segmentedControl {
+            
+            for (index, model) in models.enumerate() {
+                
+                segmentedControl.setTitle(
+                    model.label,
+                    forSegmentAtIndex: index
+                )
+            }
+        }
+        
+        let dataStack = DataStack(modelName: "MigrationDemo")
+        do {
+            
+            let migrations = try dataStack.requiredMigrationsForSQLiteStore(
+                fileName: "MigrationDemo.sqlite"
+            )
+            
+            let storeVersion = migrations.first?.sourceVersion ?? dataStack.modelVersion
+            for model in models {
+                
+                if model.version == storeVersion {
+                    
+                    self.selectModelVersion(model, animated: false)
+                    return
+                }
+            }
+        }
+        catch _ { }
+        
+        self.selectModelVersion(self.models.first!, animated: false)
     }
     
 
@@ -47,21 +79,23 @@ class MigrationsDemoViewController: UITableViewController {
 
     override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
         
-        self.selectModelVersion(self.models[indexPath.row])
+        self.selectModelVersion(self.models[indexPath.row], animated: true)
     }
     
     
     // MARK: Private
     
-    private typealias ModelMetadata = (version: String, entityType: AnyClass, migrationChain: MigrationChain)
+    private typealias ModelMetadata = (label: String, version: String, entityType: AnyClass, migrationChain: MigrationChain)
     
     private let models: [ModelMetadata] = [
         (
+            label: "Model V1",
             version: "MigrationDemo",
             entityType: OrganismV1.self,
             migrationChain: ["MigrationDemoV3", "MigrationDemoV2", "MigrationDemo"]
         ),
         (
+            label: "Model V2",
             version: "MigrationDemoV2",
             entityType: OrganismV2.self,
             migrationChain: [
@@ -70,6 +104,7 @@ class MigrationsDemoViewController: UITableViewController {
             ]
         ),
         (
+            label: "Model V3",
             version: "MigrationDemoV3",
             entityType: OrganismV3.self,
             migrationChain: ["MigrationDemo", "MigrationDemoV2", "MigrationDemoV3"]
@@ -81,6 +116,8 @@ class MigrationsDemoViewController: UITableViewController {
     
     @IBOutlet private dynamic weak var titleLabel: UILabel?
     @IBOutlet private dynamic weak var organismLabel: UILabel?
+    @IBOutlet private dynamic weak var segmentedControl: UISegmentedControl?
+    @IBOutlet private dynamic weak var progressView: UIProgressView?
     
     @IBAction private dynamic func mutateBarButtonTapped(sender: AnyObject?) {
         
@@ -93,11 +130,21 @@ class MigrationsDemoViewController: UITableViewController {
                 
                 transaction.commit()
             }
-            self.updateDisplay()
+            self.updateDisplayWithCompletion()
         }
     }
     
-    private func selectModelVersion(model: ModelMetadata) {
+    @IBAction private dynamic func segmentedControlValueChanged(sender: AnyObject?) {
+        
+        guard let index = self.segmentedControl?.selectedSegmentIndex else {
+            
+            return
+        }
+        
+        self.selectModelVersion(self.models[index], animated: true)
+    }
+    
+    private func selectModelVersion(model: ModelMetadata, animated: Bool) {
         
         if self.organism?.entity.managedObjectClassName == "\(model.entityType)" {
             
@@ -112,8 +159,8 @@ class MigrationsDemoViewController: UITableViewController {
             migrationChain: model.migrationChain
         )
         
-        self.setEnabled(false)
+        self.setEnabled(false, animated: animated)
-        dataStack.addSQLiteStore(
+        let progress = try! dataStack.addSQLiteStore(
             fileName: "MigrationDemo.sqlite",
             completion: { [weak self] (result) -> Void in
                 
@@ -124,7 +171,7 @@ class MigrationsDemoViewController: UITableViewController {
                 
                 guard case .Success = result else {
                     
-                    strongSelf.setEnabled(true)
+                    strongSelf.setEnabled(true, animated: animated)
                     return
                 }
                 
@@ -137,32 +184,44 @@ class MigrationsDemoViewController: UITableViewController {
                     
                     dataStack.beginSynchronous { (transaction) -> Void in
                         
-                        let organism = transaction.create(Into(model.entityType))
+                        for _ in 0 ..< 100000 {
-                        (organism as! OrganismProtocol).mutate()
+                            
+                            let organism = transaction.create(Into(model.entityType))
+                            (organism as! OrganismProtocol).mutate()
+                        }
                         
                         transaction.commit()
                     }
                     strongSelf.organism = dataStack.fetchOne(From(model.entityType))!
                 }
                 
-                strongSelf.updateDisplay()
+                strongSelf.updateDisplayWithCompletion()
+                
+                let indexOfModel = strongSelf.models.map { $0.version }.indexOf(model.version)!
                 strongSelf.tableView.selectRowAtIndexPath(
-                    NSIndexPath(
+                    NSIndexPath(forRow: indexOfModel, inSection: 0),
-                        forRow: strongSelf.models.map { $0.version }.indexOf(model.version)!,
-                        inSection: 0
-                    ),
                     animated: false,
                     scrollPosition: .None
                 )
-                strongSelf.setEnabled(true)
+                strongSelf.segmentedControl?.selectedSegmentIndex = indexOfModel
+                strongSelf.setEnabled(true, animated: animated)
             }
         )
+        
+        if let progress = progress {
+            
+            self.updateDisplayWithProgress(progress)
+            progress.setProgressHandler { [weak self] (progress) -> Void in
+                
+                self?.updateDisplayWithProgress(progress)
+            }
+        }
     }
     
-    func setEnabled(enabled: Bool) {
+    func setEnabled(enabled: Bool, animated: Bool) {
         
         UIView.animateKeyframesWithDuration(
-            0.2,
+            animated ? 0.2 : 0,
             delay: 0,
             options: .BeginFromCurrentState,
             animations: { () -> Void in
@@ -182,7 +241,14 @@ class MigrationsDemoViewController: UITableViewController {
         )
     }
     
-    func updateDisplay() {
+    func updateDisplayWithProgress(progress: NSProgress) {
+        
+        self.progressView?.setProgress(Float(progress.fractionCompleted), animated: true)
+        self.titleLabel?.text = "Migrating: \(progress.localizedDescription)"
+        self.organismLabel?.text = "Incremental step \(progress.localizedAdditionalDescription)"
+    }
+    
+    func updateDisplayWithCompletion() {
         
         var lines = [String]()
         var organismType = ""
@@ -193,11 +259,12 @@ class MigrationsDemoViewController: UITableViewController {
                 let value: AnyObject = organism.valueForKey(property.name) ?? NSNull()
                 lines.append("\(property.name): \(value)")
             }
-            organismType = "\(objc_getClass(organism.entity.managedObjectClassName))"
+            organismType = organism.entity.managedObjectClassName
         }
         
         self.titleLabel?.text = organismType
         self.organismLabel?.text = "\n".join(lines)
+        self.progressView?.progress = 0
         self.tableView.tableHeaderView?.setNeedsLayout()
     }
 }