如何通过 Persistent History Tracking 观察 SwiftData 的数据变化

import Foundation
import SwiftData
import SwiftDataKit

public final class DataProvider: @unchecked Sendable {
    public var container: ModelContainer
    // a model actor to handle persistent history tracking transaction
    private var monitor: DBMonitor?

    public static let share = DataProvider(inMemory: false, enableMonitor: true)
    public static let preview = DataProvider(inMemory: true, enableMonitor: false)

    init(inMemory: Bool = false, enableMonitor: Bool = false) {
        let schema = Schema([
            Item.self,
        ])
        let modelConfiguration: ModelConfiguration
        modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: inMemory)
        do {
            let container = try ModelContainer(for: schema, configurations: [modelConfiguration])
            self.container = container
        } catch {
            fatalError("Could not create ModelContainer: \(error)")
        }
    }
}

extension DataProvider {
    @MainActor
    private func setAuthor(container: ModelContainer, authorName: String) {
        container.mainContext.managedObjectContext?.transactionAuthor = authorName
    }
}

// in init
do {
    let container = try ModelContainer(for: schema, configurations: [modelConfiguration])
    self.container = container
    // 设置 mainContext 的 transactionAuthor 为 mainApp
    Task {
        await setAuthor(container: container, authorName: "mainApp")
    }
} catch {
    fatalError("Could not create ModelContainer: \(error)")
}

import Foundation
import SwiftData
import SwiftDataKit
import Combine
import CoreData

@ModelActor
public actor DBMonitor {
    private var cancellable: AnyCancellable?
    // 最后历史事务时间戳
    private var lastHistoryTransactionTimestamp: Date {
        get {
            UserDefaults.standard.object(forKey: "lastHistoryTransactionTimestamp") as? Date ?? Date.distantPast
        }
        set {
            UserDefaults.standard.setValue(newValue, forKey: "lastHistoryTransactionTimestamp")
        }
    }
}

extension DBMonitor {
    // 响应持久历史跟踪通知
    public func register(excludeAuthors: [String] = []) {
        guard let coordinator = modelContext.coordinator else { return }
        cancellable = NotificationCenter.default.publisher(
            for: .NSPersistentStoreRemoteChange,
            object: coordinator
        )
        .map { _ in () }
        .prepend(())
        .sink { _ in
            self.processor(excludeAuthors: excludeAuthors)
        }
    }

    // 收到通知后，处理交易
    private func processor(excludeAuthors: [String]) {
        // 获取自上次时间戳后的所有事务
        let transactions = fetchTransaction()
        // 保存最新的时间戳
        lastHistoryTransactionTimestamp = transactions.max { $1.timestamp > $0.timestamp }?.timestamp ?? .now
        // 筛选事务，排除所有由 excludeAuthors 产生的事务
        for transaction in transactions where !excludeAuthors.contains([transaction.author ?? ""]) {
            for change in transaction.changes ?? [] {
                // 将事务的 change 发送给处理单元
                changeHandler(change)
            }
        }
    }

    // 获取自上次处理以来所有新生成的事务
    private func fetchTransaction() -> [NSPersistentHistoryTransaction] {
        let timestamp = lastHistoryTransactionTimestamp
        let fetchRequest = NSPersistentHistoryChangeRequest.fetchHistory(after: timestamp)
        // 在 SwiftData 中，fetchHistory 创建的 fetchRequest.fetchRequest 为 nil，无法设置 predicate
        guard let historyResult = try? modelContext.managedObjectContext?.execute(fetchRequest) as? NSPersistentHistoryResult,
              let transactions = historyResult.result as? [NSPersistentHistoryTransaction]
        else {
            return []
        }
        return transactions
    }

    // Process filtered transactions
    private func changeHandler(_ change: NSPersistentHistoryChange) {
        // 通过 SwiftDataKit ，将 NSManagedObjectID 转换为 PersistentIdentifier
        if let id = change.changedObjectID.persistentIdentifier {
            let author = change.transaction?.author ?? "unknown"
            let changeType = change.changeType
            print("author:\(author)  changeType:\(changeType)")
            print(id)
        }
    }
}

// DataProvider init
do {
    let container = try ModelContainer(for: schema, configurations: [modelConfiguration])
    self.container = container
    Task {
        await setAuthor(container: container, authorName: "mainApp")
    }
    // 创建 DBMonitor，处理持久化历史跟踪事务
    if enableMonitor {
        Task.detached {
            self.monitor = DBMonitor(modelContainer: container)
            await self.monitor?.register(excludeAuthors: ["mainApp"])
        }
    }
} catch {
    fatalError("Could not create ModelContainer: \(error)")
}

Capture of 'self' with non-sendable type 'DataProvider' in a `@Sendable` closure

@ModelActor
actor PrivateDataHandler {
    func setAuthorName(name: String) {
        modelContext.managedObjectContext?.transactionAuthor = name
    }

    func newItem() {
        let item = Item(timestamp: .now)
        modelContext.insert(item)
        try? modelContext.save()
    }
}

ToolbarItem(placement: .topBarLeading) {
    Button {
        let container = modelContext.container
        Task.detached {
            let handler = PrivateDataHandler(modelContainer: container)
            // 将 PrivateDataHandler 的 modelContext 的 transactionAuthor 设置为 Private，也可以不设置
            await handler.setAuthorName(name: "Private")
            await handler.newItem()
        }
    } label: {
        Text("New Item")
    }
}