Migrations demo done

Demo/⭐️Sources/Helpers/Menu/Menu.MainView.swift

@@ -96,9 +96,10 @@ extension Menu {
                         Menu.ItemView(
                             title: "Evolution",
                             subtitle: "Migrating and reverse-migrating stores",
-                            destination: { EmptyView() }
+                            destination: {
+                                Advanced.EvolutionDemo.MainView()
+                            }
                         )
-                        .disabled(true)
                         Menu.ItemView(
                             title: "Logger",
                             subtitle: "Implementing a custom logger",

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.CreatureType.swift

@@ -18,7 +18,13 @@ extension Advanced.EvolutionDemo {
 
 protocol Advanced_EvolutionDemo_CreatureType: DynamicObject, CustomStringConvertible {
 
-    var dnaCode: Int64 { get }
+    var dnaCode: Int64 { get set }
+
+    static func dataSource(in dataStack: DataStack) -> Advanced.EvolutionDemo.CreaturesDataSource
+
+    static func count(in transaction: BaseDataTransaction) throws -> Int
+
+    static func create(in transaction: BaseDataTransaction) -> Self
 
     func mutate(in transaction: BaseDataTransaction)
 }

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.CreaturesDataSource.swift

@@ -0,0 +1,165 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+import Combine
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    // MARK: - Advanced.EvolutionDemo.CreaturesDataSource
+
+    final class CreaturesDataSource: ObservableObject {
+
+        // MARK: Internal
+
+        init<T: NSManagedObject & Advanced.EvolutionDemo.CreatureType>(
+            listPublisher: ListPublisher<T>,
+            dataStack: DataStack
+        ) {
+
+            self.numberOfItems = {
+                listPublisher.snapshot.numberOfItems
+            }
+            self.itemDescriptionAtIndex = { index in
+                listPublisher.snapshot[index].object?.description
+            }
+            self.addItems = { count in
+
+                dataStack.perform(
+                    asynchronous: { transaction in
+
+                        let nextDNACode = try transaction.fetchCount(From<T>())
+                        for offset in 0 ..< count {
+
+                            let object = transaction.create(Into<T>())
+                            object.dnaCode = .init(nextDNACode + offset)
+                            object.mutate(in: transaction)
+                        }
+                    },
+                    completion: { _ in }
+                )
+            }
+            self.mutateItemAtIndex = { index in
+
+                let object = listPublisher.snapshot[index]
+                dataStack.perform(
+                    asynchronous: { transaction in
+
+                        object
+                            .asEditable(in: transaction)?
+                            .mutate(in: transaction)
+                    },
+                    completion: { _ in }
+                )
+            }
+            self.deleteAllItems = {
+
+                dataStack.perform(
+                    asynchronous: { transaction in
+
+                        try transaction.deleteAll(From<T>())
+                    },
+                    completion: { _ in }
+                )
+            }
+            listPublisher.addObserver(self) { [weak self] (listPublisher) in
+
+                self?.objectWillChange.send()
+            }
+        }
+
+        init<T: CoreStoreObject & Advanced.EvolutionDemo.CreatureType>(
+            listPublisher: ListPublisher<T>,
+            dataStack: DataStack
+        ) {
+
+            self.numberOfItems = {
+                listPublisher.snapshot.numberOfItems
+            }
+            self.itemDescriptionAtIndex = { index in
+                listPublisher.snapshot[index].object?.description
+            }
+            self.addItems = { count in
+
+                dataStack.perform(
+                    asynchronous: { transaction in
+
+                        let nextDNACode = try transaction.fetchCount(From<T>())
+                        for offset in 0 ..< count {
+
+                            let object = transaction.create(Into<T>())
+                            object.dnaCode = .init(nextDNACode + offset)
+                            object.mutate(in: transaction)
+                        }
+                    },
+                    completion: { _ in }
+                )
+            }
+            self.mutateItemAtIndex = { index in
+
+                let object = listPublisher.snapshot[index]
+                dataStack.perform(
+                    asynchronous: { transaction in
+
+                        object
+                            .asEditable(in: transaction)?
+                            .mutate(in: transaction)
+                    },
+                    completion: { _ in }
+                )
+            }
+            self.deleteAllItems = {
+
+                dataStack.perform(
+                    asynchronous: { transaction in
+
+                        try transaction.deleteAll(From<T>())
+                    },
+                    completion: { _ in }
+                )
+            }
+            listPublisher.addObserver(self) { [weak self] (listPublisher) in
+
+                self?.objectWillChange.send()
+            }
+        }
+
+        func numberOfCreatures() -> Int {
+
+            return self.numberOfItems()
+        }
+
+        func creatureDescription(at index: Int) -> String? {
+
+            return self.itemDescriptionAtIndex(index)
+        }
+
+        func mutate(at index: Int) {
+
+            self.mutateItemAtIndex(index)
+        }
+
+        func add(count: Int) {
+
+            self.addItems(count)
+        }
+
+        func clear() {
+
+            self.deleteAllItems()
+        }
+
+
+        // MARK: Private
+
+        private let numberOfItems: () -> Int
+        private let itemDescriptionAtIndex: (Int) -> String?
+        private let mutateItemAtIndex: (Int) -> Void
+        private let addItems: (Int) -> Void
+        private let deleteAllItems: () -> Void
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.GeologicalPeriod.swift

@@ -2,13 +2,17 @@
 // Demo
 // Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
 
+import CoreStore
+
+
 // MARK: - AdvancedEvolutionDemo
 
 extension Advanced.EvolutionDemo {
     
     // MARK: - GeologicalPeriod
     
-    enum GeologicalPeriod: CaseIterable {
+    enum GeologicalPeriod: RawRepresentable, CaseIterable, Hashable, CustomStringConvertible {
+
 
         // MARK: Internal
         
@@ -17,6 +21,11 @@ extension Advanced.EvolutionDemo {
         case ageOfReptiles
         case ageOfMammals
 
+        var version: ModelVersion {
+
+            return self.rawValue
+        }
+
         var creatureType: Advanced.EvolutionDemo.CreatureType.Type {
 
             switch self {
@@ -31,5 +40,60 @@ extension Advanced.EvolutionDemo {
                 return Advanced.EvolutionDemo.V4.Creature.self
             }
         }
+
+
+        // MARK: CustomStringConvertible
+
+        var description: String {
+
+            switch self {
+
+            case .ageOfInvertebrates:
+                return "Invertebrates"
+            case .ageOfFishes:
+                return "Fishes"
+            case .ageOfReptiles:
+                return "Reptiles"
+            case .ageOfMammals:
+                return "Mammals"
+            }
+        }
+
+
+        // MARK: RawRepresentable
+
+        typealias RawValue = ModelVersion
+
+        var rawValue: ModelVersion {
+
+            switch self {
+
+            case .ageOfInvertebrates:
+                return Advanced.EvolutionDemo.V1.name
+            case .ageOfFishes:
+                return Advanced.EvolutionDemo.V2.name
+            case .ageOfReptiles:
+                return Advanced.EvolutionDemo.V3.name
+            case .ageOfMammals:
+                return Advanced.EvolutionDemo.V4.name
+            }
+        }
+
+        init?(rawValue: ModelVersion) {
+
+            switch rawValue {
+
+            case Advanced.EvolutionDemo.V1.name:
+                self = .ageOfInvertebrates
+            case Advanced.EvolutionDemo.V2.name:
+                self = .ageOfFishes
+            case Advanced.EvolutionDemo.V3.name:
+                self = .ageOfReptiles
+            case Advanced.EvolutionDemo.V4.name:
+                self = .ageOfMammals
+            default:
+                return nil
+            }
+        }
     }
 }

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.ItemView.swift

@@ -2,4 +2,74 @@
 // Demo
 // Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
 
-import Foundation
+import SwiftUI
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    // MARK: - Advanced.EvolutionDemo.ItemView
+
+    struct ItemView: View {
+
+        // MARK: Internal
+
+        init(description: String?, mutate: @escaping () -> Void) {
+            
+            self.description = description
+            self.mutate = mutate
+        }
+
+
+        // MARK: View
+
+        var body: some View {
+            HStack {
+                Text(self.description ?? "")
+                    .font(.footnote)
+                    .foregroundColor(.primary)
+                Spacer()
+                Button(
+                    action: self.mutate,
+                    label: {
+                        Text("Mutate")
+                            .foregroundColor(.accentColor)
+                            .fontWeight(.bold)
+                    }
+                )
+                .buttonStyle(PlainButtonStyle())
+            }
+            .disabled(self.description == nil)
+        }
+
+
+        // MARK: FilePrivate
+
+        fileprivate let description: String?
+        fileprivate let mutate: () -> Void
+    }
+}
+
+#if DEBUG
+
+struct _Demo_Advanced_EvolutionDemo_ItemView_Preview: PreviewProvider {
+
+    // MARK: PreviewProvider
+
+    static var previews: some View {
+        Advanced.EvolutionDemo.ItemView(
+            description: """
+                dnaCode: 123
+                numberOfLimbs: 4
+                hasVertebrae: true
+                hasHead: true
+                hasTail: true
+                habitat: land
+                hasWings: false
+                """,
+            mutate: {}
+        )
+    }
+}
+
+#endif

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.ListView.swift

@@ -2,4 +2,98 @@
 // Demo
 // Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
 
-import Foundation
+import CoreStore
+import SwiftUI
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    // MARK: - Advanced.EvolutionDemo.ListView
+
+    struct ListView: View {
+
+        // MARK: View
+
+        var body: some View {
+            let dataSource = self.dataSource
+            return List {
+                ForEach(0 ..< dataSource.numberOfCreatures(), id: \.self) { (index) in
+                    Advanced.EvolutionDemo.ItemView(
+                        description: dataSource.creatureDescription(at: index),
+                        mutate: {
+
+                            dataSource.mutate(at: index)
+                        }
+                    )
+                }
+            }
+            .listStyle(PlainListStyle())
+        }
+
+
+        // MARK: Internal
+
+        init(
+            period: Advanced.EvolutionDemo.GeologicalPeriod,
+            dataStack: DataStack,
+            dataSource: Advanced.EvolutionDemo.CreaturesDataSource
+        ) {
+
+            self.period = period
+            self.dataStack = dataStack
+            self.dataSource = dataSource
+        }
+
+
+        // MARK: Private
+
+        private let period: Advanced.EvolutionDemo.GeologicalPeriod
+
+        private let dataStack: DataStack
+
+        @ObservedObject
+        private var dataSource: Advanced.EvolutionDemo.CreaturesDataSource
+    }
+}
+
+
+#if DEBUG
+
+struct _Demo_Advanced_EvolutionDemo_ListView_Preview: PreviewProvider {
+
+    // MARK: PreviewProvider
+
+    static var previews: some View {
+
+        let dataStack = DataStack(
+            CoreStoreSchema(
+                modelVersion: Advanced.EvolutionDemo.V4.name,
+                entities: [
+                    Entity<Advanced.EvolutionDemo.V4.Creature>("Creature")
+                ]
+            )
+        )
+        try! dataStack.addStorageAndWait(
+            SQLiteStore(fileName: "Advanced.EvolutionDemo.ListView.Preview.sqlite")
+        )
+        try! dataStack.perform(
+            synchronous: { transaction in
+
+                for dnaCode in 0 ..< 10 as Range<Int64> {
+
+                    let object = transaction.create(Into<Advanced.EvolutionDemo.V4.Creature>())
+                    object.dnaCode = dnaCode
+                    object.mutate(in: transaction)
+                }
+            }
+        )
+        return Advanced.EvolutionDemo.ListView(
+            period: .ageOfMammals,
+            dataStack: dataStack,
+            dataSource: Advanced.EvolutionDemo.V4.Creature.dataSource(in: dataStack)
+        )
+    }
+}
+
+#endif

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.MainView.swift

@@ -2,4 +2,77 @@
 // Demo
 // Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
 
-import Foundation
+import CoreStore
+import SwiftUI
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    // MARK: - Advanced.EvolutionDemo.MainView
+
+    struct MainView: View {
+
+        // MARK: View
+
+        var body: some View {
+            let migrator = self.migrator
+            let listView: AnyView
+            if let current = migrator.current {
+
+                listView = AnyView(
+                    Advanced.EvolutionDemo.ListView(
+                        period: current.period,
+                        dataStack: current.dataStack,
+                        dataSource: current.dataSource
+                    )
+                )
+            }
+            else {
+
+                listView = AnyView(
+                    Advanced.EvolutionDemo.ProgressView(progress: migrator.progress)
+                )
+            }
+
+            return VStack(spacing: 0) {
+                    HStack(alignment: .center, spacing: 0) {
+                        Text("Age of")
+                            .padding(.trailing)
+                        Picker(selection: self.$migrator.currentPeriod, label: EmptyView()) {
+                            ForEach(Advanced.EvolutionDemo.GeologicalPeriod.allCases, id: \.self) { period in
+                                Text(period.description).tag(period)
+                            }
+                        }
+                        .pickerStyle(SegmentedPickerStyle())
+                    }
+                    .padding()
+                    listView
+                        .edgesIgnoringSafeArea(.vertical)
+                }
+                .navigationBarTitle("Evolution")
+                .disabled(migrator.isBusy || migrator.current == nil)
+        }
+
+
+        // MARK: Private
+
+        @ObservedObject
+        private var migrator: Advanced.EvolutionDemo.Migrator = .init()
+    }
+}
+
+
+#if DEBUG
+
+struct _Demo_Advanced_EvolutionDemo_MainView_Preview: PreviewProvider {
+
+    // MARK: PreviewProvider
+
+    static var previews: some View {
+
+        Advanced.EvolutionDemo.MainView()
+    }
+}
+
+#endif

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.Migrator.swift

@@ -14,34 +14,20 @@ extension Advanced.EvolutionDemo {
     // MARK: - Advanced.EvolutionDemo.Migrator
     
     final class Migrator: ObservableObject {
-        
-        var currentPeriod: Advanced.EvolutionDemo.GeologicalPeriod? {
-            
-            return self.current?.period
-        }
-        
-        
-        // MARK: Private
-        
-        private var current: (period: Advanced.EvolutionDemo.GeologicalPeriod, dataStack: DataStack)? {
-            
-            willSet {
-                
-                self.objectWillChange.send()
-            }
-        }
-        
-        private func findAndSetCurrentVersion() {
-            
+
+        /**
+         ⭐️ Sample 1: Creating a complex `DataStack` that contains all schema histories. The `exactCurrentModelVersion` will specify the target version (if required), and `migrationChain` will provide the upgrade/downgrade progressive migration path.
+         */
+        private func createDataStack(
+            exactCurrentModelVersion: ModelVersion?,
+            migrationChain: MigrationChain
+        ) -> DataStack {
+
             let xcodeV1ToV2ModelSchema = XcodeDataModelSchema.from(
                 modelName: "Advanced.EvolutionDemo.V1",
-                bundle: Bundle(for: Advanced.EvolutionDemo.V1.Creature.self),
-                migrationChain: [
-                    Advanced.EvolutionDemo.V1.name,
-                    Advanced.EvolutionDemo.V2.name
-                ]
+                bundle: Bundle(for: Advanced.EvolutionDemo.V1.Creature.self)
             )
-            let dataStack = DataStack(
+            return DataStack(
                 schemaHistory: SchemaHistory(
                     allSchema: xcodeV1ToV2ModelSchema.allSchema
                     + [
@@ -58,26 +44,196 @@ extension Advanced.EvolutionDemo {
                             ]
                         )
                     ],
-                    migrationChain: [
-                        Advanced.EvolutionDemo.V1.name,
-                        Advanced.EvolutionDemo.V2.name,
-                        Advanced.EvolutionDemo.V3.name,
-                        Advanced.EvolutionDemo.V4.name
-                    ]
+                    migrationChain: migrationChain,
+                    exactCurrentModelVersion: exactCurrentModelVersion
                 )
             )
         }
+
+        /**
+         ⭐️ Sample 2: Creating a complex `SQLiteStore` that contains all schema mappings for both upgrade and downgrade cases.
+         */
+        private func accessSQLiteStore() -> SQLiteStore {
+
+            let upgradeMappings: [SchemaMappingProvider] = [
+                Advanced.EvolutionDemo.V2.FromV1.mapping,
+                Advanced.EvolutionDemo.V3.FromV2.mapping,
+                Advanced.EvolutionDemo.V4.FromV3.mapping
+            ]
+            let downgradeMappings: [SchemaMappingProvider] = [
+                Advanced.EvolutionDemo.V3.FromV4.mapping,
+                Advanced.EvolutionDemo.V2.FromV3.mapping,
+                Advanced.EvolutionDemo.V1.FromV2.mapping,
+            ]
+            return SQLiteStore(
+                fileName: "Advanced.EvolutionDemo.sqlite",
+                configuration: nil,
+                migrationMappingProviders: upgradeMappings + downgradeMappings,
+                localStorageOptions: []
+            )
+        }
+
+
+        // MARK: Internal
+
+        var currentPeriod: Advanced.EvolutionDemo.GeologicalPeriod = Advanced.EvolutionDemo.GeologicalPeriod.allCases.last! {
+
+            didSet {
+
+                self.selectModelVersion(self.currentPeriod)
+            }
+        }
+
+        private(set) var current: (
+            period: Advanced.EvolutionDemo.GeologicalPeriod,
+            dataStack: DataStack,
+            dataSource: Advanced.EvolutionDemo.CreaturesDataSource
+        )? {
+
+            willSet {
+
+                self.objectWillChange.send()
+            }
+        }
+
+        private(set) var isBusy: Bool = false
+
+        private(set) var progress: Progress?
+
+
+        init() {
+
+            self.synchronizeCurrentVersion()
+        }
         
-        private func selectModelVersion(_ period: GeologicalPeriod) {
-            
-            guard period != self.current?.period else {
+        
+        // MARK: Private
+        
+        private func synchronizeCurrentVersion() {
+
+            // Since we are only interested in finding current version, we'll assume an upgrading `MigrationChain`
+            let dataStack = self.createDataStack(
+                exactCurrentModelVersion: nil,
+                migrationChain: MigrationChain(
+                    Advanced.EvolutionDemo.GeologicalPeriod.allCases.map({ $0.version })
+                )
+            )
+            let migrations = try! dataStack.requiredMigrationsForStorage(
+                self.accessSQLiteStore()
+            )
+            if let period = migrations.first
+                .flatMap({ Advanced.EvolutionDemo.GeologicalPeriod(rawValue: $0.sourceVersion) }) {
+
+                self.selectModelVersion(period)
+            }
+            else {
+
+                self.selectModelVersion(self.currentPeriod)
+            }
+        }
+        
+        private func selectModelVersion(_ period: Advanced.EvolutionDemo.GeologicalPeriod) {
+
+            let currentPeriod = self.current?.period
+            guard period != currentPeriod else {
                 
                 return
             }
+
+            self.objectWillChange.send()
+
+            self.isBusy = true
             
             // explicitly trigger `NSPersistentStore` cleanup by deallocating the `DataStack`
             self.current = nil
-            
+
+            let migrationChain: MigrationChain
+            switch (currentPeriod?.version, period.version) {
+
+            case (nil, let newVersion):
+                migrationChain = [newVersion]
+
+            case (let currentVersion?, let newVersion):
+                let upgradeMigrationChain = Advanced.EvolutionDemo.GeologicalPeriod.allCases
+                    .map({ $0.version })
+                let currentVersionIndex = upgradeMigrationChain.firstIndex(of: currentVersion)!
+                let newVersionIndex = upgradeMigrationChain.firstIndex(of: newVersion)!
+
+                migrationChain = MigrationChain(
+                    currentVersionIndex > newVersionIndex
+                        ? upgradeMigrationChain.reversed()
+                        : upgradeMigrationChain
+                )
+            }
+            let dataStack = self.createDataStack(
+                exactCurrentModelVersion: period.version,
+                migrationChain: migrationChain
+            )
+
+            let completion = { [weak self] () -> Void in
+
+                guard let self = self else {
+
+                    return
+                }
+                self.objectWillChange.send()
+                defer {
+
+                    self.isBusy = false
+                }
+                self.current = (
+                    period: period,
+                    dataStack: dataStack,
+                    dataSource: period.creatureType.dataSource(in: dataStack)
+                )
+                self.currentPeriod = period
+            }
+
+            self.progress = dataStack.addStorage(
+                self.accessSQLiteStore(),
+                completion: { [weak self] result in
+
+                    guard let self = self else {
+
+                        return
+                    }
+                    guard case .success = result else {
+
+                        self.objectWillChange.send()
+                        self.isBusy = false
+                        return
+                    }
+                    if self.progress == nil {
+
+                        self.spawnCreatures(in: dataStack, period: period, completion: completion)
+                    }
+                    else {
+
+                        completion()
+                    }
+                }
+            )
+        }
+
+        private func spawnCreatures(
+            in dataStack: DataStack,
+            period: Advanced.EvolutionDemo.GeologicalPeriod,
+            completion: @escaping () -> Void
+        ) {
+
+            dataStack.perform(
+                asynchronous: { (transaction) in
+
+                    let creatureType = period.creatureType
+                    for dnaCode in try creatureType.count(in: transaction) ..< 10000 {
+
+                        let object = creatureType.create(in: transaction)
+                        object.dnaCode = Int64(dnaCode)
+                        object.mutate(in: transaction)
+                    }
+                },
+                completion: { _ in completion() }
+            )
         }
         
         

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.ProgressView.swift

@@ -0,0 +1,127 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import SwiftUI
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    // MARK: - Advanced.EvolutionDemo.ProgressView
+
+    struct ProgressView: View {
+
+        // MARK: Internal
+
+        init(progress: Progress?) {
+
+            self.progressObserver = .init(progress)
+        }
+
+
+        // MARK: View
+
+        var body: some View {
+
+            guard self.progressObserver.isMigrating else {
+
+                return AnyView(
+                    VStack(alignment: .center) {
+                        Text("Preparing creatures...")
+                            .padding()
+                        Spacer()
+                    }
+                    .padding()
+                )
+            }
+            return AnyView(
+                VStack(alignment: .leading) {
+                    Text("Migrating: \(self.progressObserver.localizedDescription)")
+                        .font(.headline)
+                        .padding([.top, .horizontal])
+                    Text("Progressive step: \(self.progressObserver.localizedAdditionalDescription)")
+                        .font(.subheadline)
+                        .padding(.horizontal)
+                    GeometryReader { geometry in
+                        ZStack(alignment: .leading) {
+                            Color.gray
+                                .opacity(0.2)
+                                .frame(width: geometry.size.width, height: 8)
+                                .cornerRadius(4.0)
+                            Color.blue
+                                .frame(
+                                    width: geometry.size.width
+                                        * self.progressObserver.fractionCompleted,
+                                    height: 8
+                                )
+                                .cornerRadius(4.0)
+                        }
+                    }
+                    .fixedSize(horizontal: false, vertical: true)
+                    .padding()
+                    Spacer()
+                }
+                .padding()
+            )
+        }
+
+
+        // MARK: FilePrivate
+
+        @ObservedObject
+        private var progressObserver: ProgressObserver
+
+
+        // MARK: - ProgressObserver
+
+        fileprivate final class ProgressObserver: ObservableObject {
+
+            private(set) var fractionCompleted: CGFloat = 0
+            private(set) var localizedDescription: String = ""
+            private(set) var localizedAdditionalDescription: String = ""
+
+            var isMigrating: Bool {
+
+                return self.progress != nil
+            }
+
+            init(_ progress: Progress?) {
+
+                self.progress = progress
+
+                progress?.setProgressHandler { [weak self] (progess) in
+
+                    guard let self = self else {
+                        return
+                    }
+                    self.objectWillChange.send()
+                    self.fractionCompleted = CGFloat(progress?.fractionCompleted ?? 0)
+                    self.localizedDescription = progress?.localizedDescription ?? ""
+                    self.localizedAdditionalDescription = progress?.localizedAdditionalDescription ?? ""
+                }
+            }
+
+            // MARK: Private
+
+            private let progress: Progress?
+        }
+    }
+}
+
+#if DEBUG
+
+struct _Demo_Advanced_EvolutionDemo_ProgressView_Preview: PreviewProvider {
+
+    // MARK: PreviewProvider
+
+    static var previews: some View {
+        let progress = Progress(totalUnitCount: 10)
+        progress.completedUnitCount = 3
+        return Advanced.EvolutionDemo.ProgressView(
+            progress: progress
+        )
+    }
+}
+
+#endif

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V1.Creature.swift

@@ -30,6 +30,31 @@ final class Advanced_EvolutionDemo_V1_Creature: NSManagedObject, Advanced.Evolut
     
     
     // MARK: Advanced.EvolutionDemo.CreatureType
+
+    static func dataSource(in dataStack: DataStack) -> Advanced.EvolutionDemo.CreaturesDataSource {
+
+        return .init(
+            listPublisher: dataStack.publishList(
+                From<Advanced.EvolutionDemo.V1.Creature>()
+                    .orderBy(.descending(\.dnaCode))
+            ),
+            dataStack: dataStack
+        )
+    }
+
+    static func count(in transaction: BaseDataTransaction) throws -> Int {
+
+        return try transaction.fetchCount(
+            From<Advanced.EvolutionDemo.V1.Creature>()
+        )
+    }
+
+    static func create(in transaction: BaseDataTransaction) -> Advanced.EvolutionDemo.V1.Creature {
+
+        return transaction.create(
+            Into<Advanced.EvolutionDemo.V1.Creature>()
+        )
+    }
     
     func mutate(in transaction: BaseDataTransaction) {
         

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V1.FromV2.swift

@@ -0,0 +1,27 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V1
+
+extension Advanced.EvolutionDemo.V1 {
+
+    // MARK: - Advanced.EvolutionDemo.V1.FromV2
+
+    enum FromV2 {
+
+        // MARK: Internal
+
+        static var mapping: XcodeSchemaMappingProvider {
+
+            return XcodeSchemaMappingProvider(
+                from: Advanced.EvolutionDemo.V2.name,
+                to: Advanced.EvolutionDemo.V1.name,
+                mappingModelBundle: Bundle(for: Advanced.EvolutionDemo.V1.Creature.self)
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V1.swift

@@ -18,7 +18,7 @@ extension Advanced.EvolutionDemo {
         
         // MARK: Internal
         
-        static let name: ModelVersion = "Advanced.Evolution.V1"
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V1"
         
         typealias Creature = Advanced_EvolutionDemo_V1_Creature
     }

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V2.Creature.swift

@@ -42,6 +42,31 @@ final class Advanced_EvolutionDemo_V2_Creature: NSManagedObject, Advanced.Evolut
     
     
     // MARK: Advanced.EvolutionDemo.CreatureType
+
+    static func dataSource(in dataStack: DataStack) -> Advanced.EvolutionDemo.CreaturesDataSource {
+
+        return .init(
+            listPublisher: dataStack.publishList(
+                From<Advanced.EvolutionDemo.V2.Creature>()
+                    .orderBy(.descending(\.dnaCode))
+            ),
+            dataStack: dataStack
+        )
+    }
+
+    static func count(in transaction: BaseDataTransaction) throws -> Int {
+
+        return try transaction.fetchCount(
+            From<Advanced.EvolutionDemo.V2.Creature>()
+        )
+    }
+
+    static func create(in transaction: BaseDataTransaction) -> Advanced.EvolutionDemo.V2.Creature {
+
+        return transaction.create(
+            Into<Advanced.EvolutionDemo.V2.Creature>()
+        )
+    }
     
     func mutate(in transaction: BaseDataTransaction) {
         

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V2.FromV1.swift

@@ -0,0 +1,27 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V2
+
+extension Advanced.EvolutionDemo.V2 {
+
+    // MARK: - Advanced.EvolutionDemo.V2.FromV1
+
+    enum FromV1 {
+
+        // MARK: Internal
+
+        static var mapping: XcodeSchemaMappingProvider {
+
+            return XcodeSchemaMappingProvider(
+                from: Advanced.EvolutionDemo.V1.name,
+                to: Advanced.EvolutionDemo.V2.name,
+                mappingModelBundle: Bundle(for: Advanced.EvolutionDemo.V1.Creature.self)
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V2.FromV1MigrationPolicy.swift

@@ -0,0 +1,40 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreData
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V2.FromV1MigrationPolicy
+
+@objc(Advanced_EvolutionDemo_V2_FromV1MigrationPolicy)
+final class Advanced_EvolutionDemo_V2_FromV1MigrationPolicy: NSEntityMigrationPolicy {
+
+    // MARK: NSEntityMigrationPolicy
+
+    override func createDestinationInstances(
+        forSource sInstance: NSManagedObject,
+        in mapping: NSEntityMapping,
+        manager: NSMigrationManager
+    ) throws {
+
+        try super.createDestinationInstances(
+            forSource: sInstance,
+            in: mapping,
+            manager: manager
+        )
+
+        for dInstance in manager.destinationInstances(forEntityMappingName: mapping.name, sourceInstances: [sInstance]) {
+
+            dInstance.setValue(
+                Bool.random(),
+                forKey: #keyPath(Advanced.EvolutionDemo.V2.Creature.hasVertebrae)
+            )
+            dInstance.setValue(
+                Bool.random(),
+                forKey: #keyPath(Advanced.EvolutionDemo.V2.Creature.hasTail)
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V2.FromV3.swift

@@ -0,0 +1,41 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V2
+
+extension Advanced.EvolutionDemo.V2 {
+
+    // MARK: - Advanced.EvolutionDemo.V2.FromV3
+
+    enum FromV3 {
+
+        // MARK: Internal
+
+        static var mapping: CustomSchemaMappingProvider {
+
+            return CustomSchemaMappingProvider(
+                from: Advanced.EvolutionDemo.V3.name,
+                to: Advanced.EvolutionDemo.V2.name,
+                entityMappings: [
+                    .transformEntity(
+                        sourceEntity: "Creature",
+                        destinationEntity: "Creature",
+                        transformer: { (source, createDestination) in
+
+                            let destination = createDestination()
+                            destination["dnaCode"] = source["dnaCode"]
+                            destination["numberOfFlippers"] = source["numberOfLimbs"]
+                            destination["hasVertebrae"] = source["hasVertebrae"]
+                            destination["hasHead"] = source["hasHead"]
+                            destination["hasTail"] = source["hasTail"]
+                        }
+                    )
+                ]
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V2.swift

@@ -18,8 +18,10 @@ extension Advanced.EvolutionDemo {
         
         // MARK: Internal
         
-        static let name: ModelVersion = "Advanced.Evolution.V2"
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V2"
         
         typealias Creature = Advanced_EvolutionDemo_V2_Creature
+
+        typealias FromV1MigrationPolicy = Advanced_EvolutionDemo_V2_FromV1MigrationPolicy
     }
 }

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V3.Creature.swift

@@ -64,6 +64,31 @@ extension Advanced.EvolutionDemo.V3 {
         
         
         // MARK: Advanced.EvolutionDemo.CreatureType
+
+        static func dataSource(in dataStack: DataStack) -> Advanced.EvolutionDemo.CreaturesDataSource {
+
+            return .init(
+                listPublisher: dataStack.publishList(
+                    From<Advanced.EvolutionDemo.V3.Creature>()
+                        .orderBy(.descending(\.$dnaCode))
+                ),
+                dataStack: dataStack
+            )
+        }
+
+        static func count(in transaction: BaseDataTransaction) throws -> Int {
+
+            return try transaction.fetchCount(
+                From<Advanced.EvolutionDemo.V3.Creature>()
+            )
+        }
+
+        static func create(in transaction: BaseDataTransaction) -> Advanced.EvolutionDemo.V3.Creature {
+
+            return transaction.create(
+                Into<Advanced.EvolutionDemo.V3.Creature>()
+            )
+        }
         
         func mutate(in transaction: BaseDataTransaction) {
             

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V3.FromV2.swift

@@ -0,0 +1,43 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V3
+
+extension Advanced.EvolutionDemo.V3 {
+
+    // MARK: - Advanced.EvolutionDemo.V3.FromV2
+
+    enum FromV2 {
+
+        // MARK: Internal
+
+        static var mapping: CustomSchemaMappingProvider {
+
+            return CustomSchemaMappingProvider(
+                from: Advanced.EvolutionDemo.V2.name,
+                to: Advanced.EvolutionDemo.V3.name,
+                entityMappings: [
+                    .transformEntity(
+                        sourceEntity: "Creature",
+                        destinationEntity: "Creature",
+                        transformer: { (source, createDestination) in
+
+                            let destination = createDestination()
+                            destination["dnaCode"] = source["dnaCode"]
+                            destination["numberOfLimbs"] = source["numberOfFlippers"]
+                            destination["hasVertebrae"] = source["hasVertebrae"]
+                            destination["hasHead"] = source["hasHead"]
+                            destination["hasTail"] = source["hasTail"]
+                            destination["hasWings"] = Bool.random()
+                            destination["habitat"] = Advanced.EvolutionDemo.V3.Creature.Habitat.allCases.randomElement()!.rawValue
+                        }
+                    )
+                ]
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V3.FromV4.swift

@@ -0,0 +1,33 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V3
+
+extension Advanced.EvolutionDemo.V3 {
+
+    // MARK: - Advanced.EvolutionDemo.V3.FromV4
+
+    enum FromV4 {
+
+        // MARK: Internal
+
+        static var mapping: CustomSchemaMappingProvider {
+
+            return CustomSchemaMappingProvider(
+                from: Advanced.EvolutionDemo.V4.name,
+                to: Advanced.EvolutionDemo.V3.name,
+                entityMappings: [
+                    .transformEntity(
+                        sourceEntity: "Creature",
+                        destinationEntity: "Creature",
+                        transformer: CustomSchemaMappingProvider.CustomMapping.inferredTransformation(_:_:)
+                    )
+                ]
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V3.swift

@@ -18,6 +18,6 @@ extension Advanced.EvolutionDemo {
         
         // MARK: Internal
         
-        static let name: ModelVersion = "Advanced.Evolution.V3"
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V3"
     }
 }

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V4.Creature.swift

@@ -60,6 +60,31 @@ extension Advanced.EvolutionDemo.V4 {
         
         
         // MARK: Advanced.EvolutionDemo.CreatureType
+
+        static func dataSource(in dataStack: DataStack) -> Advanced.EvolutionDemo.CreaturesDataSource {
+
+            return .init(
+                listPublisher: dataStack.publishList(
+                    From<Advanced.EvolutionDemo.V4.Creature>()
+                        .orderBy(.descending(\.$dnaCode))
+                ),
+                dataStack: dataStack
+            )
+        }
+
+        static func count(in transaction: BaseDataTransaction) throws -> Int {
+
+            return try transaction.fetchCount(
+                From<Advanced.EvolutionDemo.V4.Creature>()
+            )
+        }
+
+        static func create(in transaction: BaseDataTransaction) -> Advanced.EvolutionDemo.V4.Creature {
+
+            return transaction.create(
+                Into<Advanced.EvolutionDemo.V4.Creature>()
+            )
+        }
         
         func mutate(in transaction: BaseDataTransaction) {
             

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V4.FromV3.swift

@@ -0,0 +1,44 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V4
+
+extension Advanced.EvolutionDemo.V4 {
+
+    // MARK: - Advanced.EvolutionDemo.V4.FromV3
+
+    enum FromV3 {
+
+        // MARK: Internal
+
+        static var mapping: CustomSchemaMappingProvider {
+
+            return CustomSchemaMappingProvider(
+                from: Advanced.EvolutionDemo.V3.name,
+                to: Advanced.EvolutionDemo.V4.name,
+                entityMappings: [
+                    .transformEntity(
+                        sourceEntity: "Creature",
+                        destinationEntity: "Creature",
+                        transformer: { (source, createDestination) in
+
+                            let destination = createDestination()
+                            destination.enumerateAttributes { (destinationAttribute, sourceAttribute) in
+
+                                if let sourceAttribute = sourceAttribute {
+
+                                    destination[destinationAttribute] = source[sourceAttribute]
+                                }
+                            }
+                            destination["isWarmBlooded"] = Bool.random()
+                        }
+                    )
+                ]
+            )
+        }
+    }
+}

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.V4.swift

@@ -18,6 +18,6 @@ extension Advanced.EvolutionDemo {
         
         // MARK: Internal
         
-        static let name: ModelVersion = "Advanced.Evolution.V4"
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V4"
     }
 }

Demo/⭐️Sources/⭐️Demos/⭐️Advanced/EvolutionDemo/Advanced.EvolutionDemo.swift

@@ -9,7 +9,7 @@ extension Advanced {
     // MARK: - Advanced.EvolutionDemo
     
     /**
-    Sample execution of progressive migrations. This demo also supports backwards migration.
+    Sample execution of progressive migrations. This demo also shows how to do two-way migration chains (upgrades+downgrades), while allowing the app to use any version of the model.
     */
     enum EvolutionDemo {}
 }