Xcode 14, iOS 16 SDK (min iOS 13)

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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+import Foundation
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    typealias CreatureType = Advanced_EvolutionDemo_CreatureType
+}
+
+
+// MARK: - Advanced.EvolutionDemo.CreatureType
+
+protocol Advanced_EvolutionDemo_CreatureType: DynamicObject, CustomStringConvertible {
+
+    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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+import Combine
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+
+    // MARK: - Advanced.EvolutionDemo.CreaturesDataSource
+
+    /**
+     A type-erasing adapter to support different `ListPublisher` types
+     */
+    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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - AdvancedEvolutionDemo
+
+extension Advanced.EvolutionDemo {
+    
+    // MARK: - GeologicalPeriod
+    
+    enum GeologicalPeriod: RawRepresentable, CaseIterable, Hashable, CustomStringConvertible {
+
+
+        // MARK: Internal
+        
+        case ageOfInvertebrates
+        case ageOfFishes
+        case ageOfReptiles
+        case ageOfMammals
+
+        var version: ModelVersion {
+
+            return self.rawValue
+        }
+
+        var creatureType: Advanced.EvolutionDemo.CreatureType.Type {
+
+            switch self {
+
+            case .ageOfInvertebrates:
+                return Advanced.EvolutionDemo.V1.Creature.self
+            case .ageOfFishes:
+                return Advanced.EvolutionDemo.V2.Creature.self
+            case .ageOfReptiles:
+                return Advanced.EvolutionDemo.V3.Creature.self
+            case .ageOfMammals:
+                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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+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

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+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+import Foundation
+import Combine
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+    
+    // MARK: - Advanced.EvolutionDemo.Migrator
+    
+    final class Migrator: ObservableObject {
+
+        /**
+         ⭐️ 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)
+            )
+            return DataStack(
+                schemaHistory: SchemaHistory(
+                    allSchema: xcodeV1ToV2ModelSchema.allSchema
+                    + [
+                        CoreStoreSchema(
+                            modelVersion: Advanced.EvolutionDemo.V3.name,
+                            entities: [
+                                Entity<Advanced.EvolutionDemo.V3.Creature>("Creature")
+                            ]
+                        ),
+                        CoreStoreSchema(
+                            modelVersion: Advanced.EvolutionDemo.V4.name,
+                            entities: [
+                                Entity<Advanced.EvolutionDemo.V4.Creature>("Creature")
+                            ]
+                        )
+                    ],
+                    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: []
+            )
+        }
+
+        /**
+         ⭐️ Sample 3: Find the model version used by an existing `SQLiteStore`, or just return the latest version if the store is not created yet.
+         */
+        private func findCurrentVersion() -> ModelVersion {
+
+            let allVersions = Advanced.EvolutionDemo.GeologicalPeriod.allCases
+                .map({ $0.version })
+
+            // Since we are only interested in finding current version, we'll assume an upgrading `MigrationChain`
+            let dataStack = self.createDataStack(
+                exactCurrentModelVersion: nil,
+                migrationChain: MigrationChain(allVersions)
+            )
+            let migrations = try! dataStack.requiredMigrationsForStorage(
+                self.accessSQLiteStore()
+            )
+
+            // If no migrations are needed, it means either the store is not created yet, or the store is already at the latest model version. In either case, we already know that the store will use the latest version
+            return migrations.first?.sourceVersion
+                ?? allVersions.last!
+        }
+
+
+        // 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()
+        }
+        
+        
+        // MARK: Private
+        
+        private func synchronizeCurrentVersion() {
+
+            guard
+                let currentPeriod = Advanced.EvolutionDemo.GeologicalPeriod(rawValue: self.findCurrentVersion())
+            else {
+
+                self.selectModelVersion(self.currentPeriod)
+                return
+            }
+            self.selectModelVersion(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() }
+            )
+        }
+        
+        
+        // MARK: - VersionMetadata
+        
+        private struct VersionMetadata {
+            
+            let label: String
+            let entityType: Advanced.EvolutionDemo.CreatureType.Type
+            let schemaHistory: SchemaHistory
+        }
+    }
+}

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

@@ -0,0 +1,126 @@
+//
+// 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) {
+                            RoundedRectangle(cornerRadius: 4, style: .continuous)
+                                .fill(Color.gray.opacity(0.2))
+                                .frame(width: geometry.size.width, height: 8)
+                            RoundedRectangle(cornerRadius: 4, style: .continuous)
+                                .fill(Color.blue)
+                                .frame(
+                                    width: geometry.size.width
+                                        * self.progressObserver.fractionCompleted,
+                                    height: 8
+                                )
+                        }
+                    }
+                    .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

@@ -0,0 +1,63 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import UIKit
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V1.Creature
+
+@objc(Advanced_EvolutionDemo_V1_Creature)
+final class Advanced_EvolutionDemo_V1_Creature: NSManagedObject, Advanced.EvolutionDemo.CreatureType {
+
+    @NSManaged
+    dynamic var dnaCode: Int64
+    
+    @NSManaged
+    dynamic var numberOfFlagella: Int32
+    
+    
+    // MARK: CustomStringConvertible
+    
+    override var description: String {
+        
+        return """
+            dnaCode: \(self.dnaCode)
+            numberOfFlagella: \(self.numberOfFlagella)
+            """
+    }
+    
+    
+    // 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) {
+        
+        self.numberOfFlagella = .random(in: 1...200)
+    }
+}

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

@@ -0,0 +1,25 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+    
+    // MARK: - Advanced.EvolutionDemo.V1
+    
+    /**
+    Namespace for V1 models (`Advanced.EvolutionDemo.GeologicalPeriod.ageOfInvertebrates`)
+    */
+    enum V1 {
+        
+        // MARK: Internal
+        
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V1"
+        
+        typealias Creature = Advanced_EvolutionDemo_V1_Creature
+    }
+}

Demo/Sources/Demos/Advanced/EvolutionDemo/Advanced.EvolutionDemo.V1.xcdatamodeld/.xccurrentversion

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>_XCCurrentVersionName</key>
+	<string>Advanced.EvolutionDemo.V1.xcdatamodel</string>
+</dict>
+</plist>

Demo/Sources/Demos/Advanced/EvolutionDemo/Advanced.EvolutionDemo.V1.xcdatamodeld/Advanced.EvolutionDemo.V1.xcdatamodel/contents

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="16119" systemVersion="19F101" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="Creature" representedClassName="Advanced_EvolutionDemo_V1_Creature" syncable="YES">
+        <attribute name="dnaCode" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
+        <attribute name="numberOfFlagella" attributeType="Integer 32" defaultValueString="2" usesScalarValueType="YES"/>
+    </entity>
+    <elements>
+        <element name="Creature" positionX="-27" positionY="18" width="128" height="73"/>
+    </elements>
+</model>

Demo/Sources/Demos/Advanced/EvolutionDemo/Advanced.EvolutionDemo.V1.xcdatamodeld/Advanced.EvolutionDemo.V2.xcdatamodel/contents

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="16119" systemVersion="19F101" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="Creature" representedClassName="Advanced_EvolutionDemo_V2_Creature" syncable="YES">
+        <attribute name="dnaCode" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
+        <attribute name="hasHead" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="hasTail" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="hasVertebrae" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="numberOfFlippers" attributeType="Integer 32" defaultValueString="2" usesScalarValueType="YES"/>
+    </entity>
+    <elements>
+        <element name="Creature" positionX="-9" positionY="36" width="128" height="118"/>
+    </elements>
+</model>

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

@@ -0,0 +1,78 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import UIKit
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo.V2.Creature
+
+@objc(Advanced_EvolutionDemo_V2_Creature)
+final class Advanced_EvolutionDemo_V2_Creature: NSManagedObject, Advanced.EvolutionDemo.CreatureType {
+
+    @NSManaged
+    dynamic var dnaCode: Int64
+    
+    @NSManaged
+    dynamic var numberOfFlippers: Int32
+    
+    @NSManaged
+    dynamic var hasVertebrae: Bool
+    
+    @NSManaged
+    dynamic var hasHead: Bool
+    
+    @NSManaged
+    dynamic var hasTail: Bool
+    
+    
+    // MARK: CustomStringConvertible
+    
+    override var description: String {
+        
+        return """
+            dnaCode: \(self.dnaCode)
+            numberOfFlippers: \(self.numberOfFlippers)
+            hasVertebrae: \(self.hasVertebrae)
+            hasHead: \(self.hasHead)
+            hasTail: \(self.hasTail)
+            """
+    }
+    
+    
+    // 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) {
+        
+        self.numberOfFlippers = .random(in: 1...4) * 2
+        self.hasVertebrae = .random()
+        self.hasHead = true
+        self.hasTail = .random()
+    }
+}

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

@@ -0,0 +1,27 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+    
+    // MARK: - Advanced.EvolutionDemo.V2
+    
+    /**
+    Namespace for V2 models (`Advanced.EvolutionDemo.GeologicalPeriod.ageOfFishes`)
+    */
+    enum V2 {
+        
+        // MARK: Internal
+        
+        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.V2.xcdatamodeld/Advanced.EvolutionDemo.V2.xcdatamodel/contents

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="16119" systemVersion="19F101" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="Creature" representedClassName="Advanced_EvolutionDemo_V2_Creature" syncable="YES">
+        <attribute name="dnaCode" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
+        <attribute name="hasHead" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="hasTail" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="hasVertebrae" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="numberOfFlippers" attributeType="Integer 32" defaultValueString="2" usesScalarValueType="YES"/>
+    </entity>
+    <elements>
+        <element name="Creature" positionX="-45" positionY="0" width="128" height="118"/>
+    </elements>
+</model>

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

@@ -0,0 +1,103 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import UIKit
+import CoreStore
+
+// MARK: - Advanced.EvolutionDemo.V3
+
+extension Advanced.EvolutionDemo.V3 {
+
+    // MARK: - Advanced.EvolutionDemo.V3.Creature
+
+    final class Creature: CoreStoreObject, Advanced.EvolutionDemo.CreatureType {
+        
+        // MARK: Internal
+
+        @Field.Stored("dnaCode")
+        var dnaCode: Int64 = 0
+
+        @Field.Stored("numberOfLimbs")
+        var numberOfLimbs: Int32 = 0
+
+        @Field.Stored("hasVertebrae")
+        var hasVertebrae: Bool = false
+
+        @Field.Stored("hasHead")
+        var hasHead: Bool = true
+
+        @Field.Stored("hasTail")
+        var hasTail: Bool = true
+
+        @Field.Stored("hasWings")
+        var hasWings: Bool = false
+
+        @Field.Stored("habitat")
+        var habitat: Habitat = .water
+        
+        
+        // MARK: - Habitat
+        
+        enum Habitat: String, CaseIterable, ImportableAttributeType, FieldStorableType {
+            
+            case water = "water"
+            case land = "land"
+            case amphibian = "amphibian"
+        }
+        
+        
+        // MARK: CustomStringConvertible
+        
+        var description: String {
+            
+            return """
+                dnaCode: \(self.dnaCode)
+                numberOfLimbs: \(self.numberOfLimbs)
+                hasVertebrae: \(self.hasVertebrae)
+                hasHead: \(self.hasHead)
+                hasTail: \(self.hasTail)
+                habitat: \(self.habitat)
+                hasWings: \(self.hasWings)
+                """
+        }
+        
+        
+        // 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) {
+            
+            self.numberOfLimbs = .random(in: 1...4) * 2
+            self.hasVertebrae = .random()
+            self.hasHead = true
+            self.hasTail = .random()
+            self.habitat = Habitat.allCases.randomElement()!
+            self.hasWings = .random()
+        }
+    }
+}

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

@@ -0,0 +1,23 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+    
+    // MARK: - Advanced.EvolutionDemo.V3
+    
+    /**
+    Namespace for V3 models (`Advanced.EvolutionDemo.GeologicalPeriod.ageOfReptiles`)
+    */
+    enum V3 {
+        
+        // MARK: Internal
+        
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V3"
+    }
+}

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

@@ -0,0 +1,100 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import UIKit
+import CoreStore
+
+// MARK: - Advanced.EvolutionDemo.V4
+
+extension Advanced.EvolutionDemo.V4 {
+
+    // MARK: - Advanced.EvolutionDemo.V4.Creature
+
+    final class Creature: CoreStoreObject, Advanced.EvolutionDemo.CreatureType {
+        
+        // MARK: Internal
+
+        @Field.Stored("dnaCode")
+        var dnaCode: Int64 = 0
+
+        @Field.Stored("numberOfLimbs")
+        var numberOfLimbs: Int32 = 0
+
+        @Field.Stored("hasVertebrae")
+        var hasVertebrae: Bool = false
+
+        @Field.Stored("hasHead")
+        var hasHead: Bool = true
+
+        @Field.Stored("hasTail")
+        var hasTail: Bool = false
+
+        @Field.Stored("hasWings")
+        var hasWings: Bool = false
+        
+        
+        typealias Habitat = Advanced.EvolutionDemo.V3.Creature.Habitat
+
+        @Field.Stored("habitat")
+        var habitat: Habitat = .water
+
+        @Field.Stored("isWarmBlooded")
+        var isWarmBlooded: Bool = true
+        
+        
+        // MARK: CustomStringConvertible
+        
+        var description: String {
+            
+            return """
+                dnaCode: \(self.dnaCode)
+                numberOfLimbs: \(self.numberOfLimbs)
+                hasVertebrae: \(self.hasVertebrae)
+                hasHead: \(self.hasHead)
+                hasTail: \(self.hasTail)
+                habitat: \(self.habitat)
+                hasWings: \(self.hasWings)
+                """
+        }
+        
+        
+        // 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) {
+            
+            self.numberOfLimbs = .random(in: 1...4) * 2
+            self.hasVertebrae = .random()
+            self.hasHead = true
+            self.hasTail = .random()
+            self.habitat = Habitat.allCases.randomElement()!
+            self.hasWings = .random()
+            self.isWarmBlooded = .random()
+        }
+    }
+}

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

@@ -0,0 +1,23 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+import CoreStore
+
+
+// MARK: - Advanced.EvolutionDemo
+
+extension Advanced.EvolutionDemo {
+    
+    // MARK: - Advanced.EvolutionDemo.V4
+    
+    /**
+    Namespace for V3 models (`Advanced.EvolutionDemo.GeologicalPeriod.ageOfMammals`)
+    */
+    enum V4 {
+        
+        // MARK: Internal
+        
+        static let name: ModelVersion = "Advanced.EvolutionDemo.V4"
+    }
+}

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

@@ -0,0 +1,24 @@
+//
+// Demo
+// Copyright © 2020 John Rommel Estropia, Inc. All rights reserved.
+
+// MARK: - Advanced
+
+extension Advanced {
+    
+    // MARK: - Advanced.EvolutionDemo
+
+    /**
+     Sample execution of progressive migrations. This example demonstrates the following concepts:
+
+     - How to inspect the current model version of the store (if it exists)
+     - How to do two-way migration chains (upgrades + downgrades)
+     - How to support multiple versions of the model on the same app
+     - How to migrate between `NSManagedObject` schema (`xcdatamodel` files) and `CoreStoreObject` schema.
+     - How to use `XcodeSchemaMappingProvider`s for `NSManagedObject` stores, and `CustomSchemaMappingProvider`s for `CoreStoreObject` stores
+     - How to manage migration models using namespacing technique
+
+     Note that ideally, your app should be supporting just the latest version of the model, and provide one-way progressive migrations from all the earlier versions.
+     */
+    enum EvolutionDemo {}
+}

Demo/Sources/Demos/Advanced/EvolutionDemo/Advanced.EvolutionDemo.xcdatamodeld/.xccurrentversion

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict/>
+</plist>

Demo/Sources/Demos/Advanced/EvolutionDemo/Advanced.EvolutionDemo.xcdatamodeld/Advanced.EvolutionDemo.V2.xcdatamodel/contents

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="16119" systemVersion="19F101" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="Creature" representedClassName="Advanced_EvolutionDemo_V1_Creature" syncable="YES" codeGenerationType="class">
+        <attribute name="dnaCode" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
+        <attribute name="numberOfFlagella" attributeType="Integer 32" defaultValueString="0" usesScalarValueType="YES"/>
+    </entity>
+    <elements>
+        <element name="Creature" positionX="-36" positionY="9" width="128" height="73"/>
+    </elements>
+</model>

Demo/Sources/Demos/Advanced/EvolutionDemo/Advanced.EvolutionDemo.xcdatamodeld/Advanced.EvolutionDemo.xcdatamodel/contents

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="16119" systemVersion="19F101" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="Creature" representedClassName="Advanced_EvolutionDemo_V1_Creature" syncable="YES" codeGenerationType="class">
+        <attribute name="dnaCode" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
+        <attribute name="numberOfFlagella" attributeType="Integer 32" defaultValueString="0" usesScalarValueType="YES"/>
+    </entity>
+    <elements>
+        <element name="Creature" positionX="-36" positionY="9" width="128" height="73"/>
+    </elements>
+</model>