iOS17+ Xcode预览含派生属性的Core Data内存存储替代方案

开发适配iOS17+与Xcode15的iOS应用及Widget扩展时，使用Core Data管理用户数据，用户实体包含一个名为lastModify（Date类型）的派生属性。在为预览提供器创建测试数据时应用崩溃，错误信息如下：

UserInfoWidgetExtension crashed due to an uncaught exception 'NSInvalidArgumentException'. Reason: Core Data provided atomic stores do not support derived

原Widget代码如下：

import WidgetKit
import SwiftUI
import Intents
import AppIntents
import CoreData

struct WidgetDetailsProvider: AppIntentTimelineProvider {
    func placeholder(in context: Context) -> SimpleEntry {
        return SimpleEntry(date: .now)
    }
    
    func snapshot(for configuration: UserInfoWidgetIntent, in context: Context) async -> SimpleEntry {
        return SimpleEntry(date: .now)
    }
    
    func timeline(for configuration: UserInfoWidgetIntent, in context: Context) async -> Timeline<SimpleEntry> {
        let entry = SimpleEntry(date: Date())
        let timeline = Timeline(entries: [entry], policy: .never)
        return timeline
    }
}

struct UserInfoWidgetIntent: WidgetConfigurationIntent {
    static var title: LocalizedStringResource = "Test"
    static var description: IntentDescription = IntentDescription("Test description")
    
    @Parameter(title: "Display in full name")
    var isDisplayFullname: Bool
    
    init(isDisplayFullname: Bool) {
        self.isDisplayFullname = isDisplayFullname
    }
    
    init() {}
}

struct SimpleEntry: TimelineEntry {
    let date: Date
    let isDisplayFullname: Bool
}

struct UserInfoWidgetEntryView : View {
    var entry: WidgetDetailsProvider.Entry
    @FetchRequest(sortDescriptors: [SortDescriptor(\.lastModify, order: .reverse)]) var userInfo: FetchedResults<UserInfo>

    var body: some View {
        VStack {
            Text(entry.date, style: .time)
                .frame(alignment: .leading)
            HStack {
                if userInfo.isEmpty {
                    Text("The list is Empty")
                }
                ForEach(userInfo) {user in
                    if entry.isDisplayFullname {
                        Text(user.fullname)
                    } else {
                        Text(user.name)
                    }
                }
            }
            
            
        }.containerBackground(for: .widget) {
            Color.white
        }
    }
}

struct UserInfoWidget: Widget {
    let kind: String = "UserInfoWidgetIntent"

    var body: some WidgetConfiguration {
        AppIntentConfiguration(
            kind: kind,
            intent: UserInfoWidgetIntent.self,
            provider: WidgetDetailsProvider()) { entry in
            UserInfoWidgetEntryView(entry: entry)
        }
        .configurationDisplayName("My Widget")
        .description("This is an example widget.")
        .supportedFamilies([.systemSmall, .systemMedium, .systemLarge])
    }
}

struct UserInfoWidget_Previews: PreviewProvider {
    static var previews: some View {
        let dummyContainer: NSPersistentContainer = {
            let container = NSPersistentContainer(name: "UserModel")
            let description = NSPersistentStoreDescription()
            description.type = NSInMemoryStoreType
            container.persistentStoreDescriptions = [description]
            container.loadPersistentStores {description, error in
                if let error = error {
                    print("Failed to load: \(error)")
                }
            }
            let dummy = Barcode(context: container.viewContext)
            dummy.username = "foo"
            do {
                try container.viewContext.save()
            } catch {
                fatalError("Failed to save entity.")
            }
            return container
        }()
        
        UserInfoWidgetEntryView(entry: SimpleEntry(date: Date()))
            .previewContext(WidgetPreviewContext(family: .systemMedium))
            .environment(\.managedObjectContext, dummyContainer.viewContext)
    }
}

移除派生属性后应用恢复正常，但希望找到无需移除派生属性的解决方案，实现在预览中使用带有派生属性的Core Data实体。

将预览中的内存存储（NSInMemoryStoreType）替换为指向/dev/null的本地存储，这样既不会持久化测试数据，又能支持派生属性。修改后的预览代码如下：

struct UserInfoWidget_Previews: PreviewProvider {
    static var previews: some View {
        let dummyContainer: NSPersistentContainer = {
            let container = NSPersistentContainer(name: "UserInfoModel")
            let description = NSPersistentStoreDescription()
            // 替换内存存储为指向/dev/null的本地存储
            description.url = URL(fileURLWithPath: "/dev/null")
            container.persistentStoreDescriptions = [description]
            container.loadPersistentStores {description, error in
                if let error = error {
                    print("Failed to load: \(error)")
                }
            }
            let dummy = UserInfo(context: container.viewContext)
            dummy.name = "foo"
            dummy.fullname = "dummy foo"
            do {
                try container.viewContext.save()
            } catch {
                fatalError("Failed to save entity.")
            }
            return container
        }()
        
        UserInfoWidgetEntryView(entry: SimpleEntry(date: Date()))
                .previewContext(WidgetPreviewContext(family: .systemSmall))
                .environment(\.managedObjectContext, dummyContainer.viewContext)
    }
}

内容的提问来源于stack exchange，提问作者KPB98115