Swift Actor Persistence

作者 affaan-mef648e01899b无许可证275K 个星标收录于 2026年10月8日更新于 2026年10月8日仓库3天前更新

Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design.

仅含说明Software Development

AI 生成的概览

使用 Swift actor 实现线程安全的本地持久化，结合内存缓存与文件存储。

功能: 提供使用 actor 构建线程安全持久化层的 Swift 代码模式，将内存字典缓存与 JSON 文件存储结合。内容包括泛型 actor 仓库及其 save、delete、find、loadAll 操作、@Observable 视图模型示例、设计决策表、最佳实践与反模式。产出为设计指导与示例代码，而非可直接运行的脚本。
适用场景: 适用于在 Swift 5.9+ 的 iOS 或 macOS 项目中构建本地数据持久化层、需要对共享可变状态进行线程安全访问、用 actor 取代手动锁或 DispatchQueue 同步，以及构建离线优先的本地存储应用。不适用于非 Swift 项目或服务端数据库工作。
运行要求: 不附带脚本或工具，仅为说明性内容。面向 Swift 5.9+ 项目（iOS 17+、macOS 14+），需要熟悉 Swift 并发、Codable 与文件存储 API。

Swift Actors for Thread-Safe Persistence

Patterns for building thread-safe data persistence layers using Swift actors. Combines in-memory caching with file-backed storage, leveraging the actor model to eliminate data races at compile time.

When to Activate

Building a data persistence layer in Swift 5.9+ (iOS 17+, macOS 14+)
Need thread-safe access to shared mutable state
Want to eliminate manual synchronization (locks, DispatchQueues)
Building offline-first apps with local storage

Core Pattern

Actor-Based Repository

The actor model guarantees serialized access — no data races, enforced by the compiler.

swift

public actor LocalRepository<T: Codable & Identifiable> where T.ID == String {    private var cache: [String: T] = [:]    private let fileURL: URL
    public init(directory: URL = .documentsDirectory, filename: String = "data.json") {        self.fileURL = directory.appendingPathComponent(filename)        // Synchronous load during init (actor isolation not yet active)        self.cache = Self.loadSynchronously(from: fileURL)    }
    // MARK: - Public API
    public func save(_ item: T) throws {        cache[item.id] = item        try persistToFile()    }
    public func delete(_ id: String) throws {        cache[id] = nil        try persistToFile()    }
    public func find(by id: String) -> T? {        cache[id]    }
    public func loadAll() -> [T] {        Array(cache.values)    }
    // MARK: - Private
    private func persistToFile() throws {        let data = try JSONEncoder().encode(Array(cache.values))        try data.write(to: fileURL, options: .atomic)    }
    private static func loadSynchronously(from url: URL) -> [String: T] {        guard let data = try? Data(contentsOf: url),              let items = try? JSONDecoder().decode([T].self, from: data) else {            return [:]        }        return Dictionary(items.map { ($0.id, $0) }, uniquingKeysWith: { _, latest in latest })    }}

public actor LocalRepository<T: Codable & Identifiable> where T.ID == String {    private var cache: [String: T] = [:]    private let fileURL: URL
    public init(directory: URL = .documentsDirectory, filename: String = "data.json") {        self.fileURL = directory.appendingPathComponent(filename)        // Synchronous load during init (actor isolation not yet active)        self.cache = Self.loadSynchronously(from: fileURL)    }
    // MARK: - Public API
    public func save(_ item: T) throws {        cache[item.id] = item        try persistToFile()    }
    public func delete(_ id: String) throws {        cache[id] = nil        try persistToFile()    }
    public func find(by id: String) -> T? {        cache[id]    }
    public func loadAll() -> [T] {        Array(cache.values)    }
    // MARK: - Private
    private func persistToFile() throws {        let data = try JSONEncoder().encode(Array(cache.values))        try data.write(to: fileURL, options: .atomic)    }
    private static func loadSynchronously(from url: URL) -> [String: T] {        guard let data = try? Data(contentsOf: url),              let items = try? JSONDecoder().decode([T].self, from: data) else {            return [:]        }        return Dictionary(items.map { ($0.id, $0) }, uniquingKeysWith: { _, latest in latest })    }}

Usage

All calls are automatically async due to actor isolation:

swift

let repository = LocalRepository<Question>()
// Read — fast O(1) lookup from in-memory cachelet question = await repository.find(by: "q-001")let allQuestions = await repository.loadAll()
// Write — updates cache and persists to file atomicallytry await repository.save(newQuestion)try await repository.delete("q-001")

let repository = LocalRepository<Question>()
// Read — fast O(1) lookup from in-memory cachelet question = await repository.find(by: "q-001")let allQuestions = await repository.loadAll()
// Write — updates cache and persists to file atomicallytry await repository.save(newQuestion)try await repository.delete("q-001")

Combining with @Observable ViewModel

swift

@Observablefinal class QuestionListViewModel {    private(set) var questions: [Question] = []    private let repository: LocalRepository<Question>
    init(repository: LocalRepository<Question> = LocalRepository()) {        self.repository = repository    }
    func load() async {        questions = await repository.loadAll()    }
    func add(_ question: Question) async throws {        try await repository.save(question)        questions = await repository.loadAll()    }}

@Observablefinal class QuestionListViewModel {    private(set) var questions: [Question] = []    private let repository: LocalRepository<Question>
    init(repository: LocalRepository<Question> = LocalRepository()) {        self.repository = repository    }
    func load() async {        questions = await repository.loadAll()    }
    func add(_ question: Question) async throws {        try await repository.save(question)        questions = await repository.loadAll()    }}

Key Design Decisions

Decision	Rationale
Actor (not class + lock)	Compiler-enforced thread safety, no manual synchronization
In-memory cache + file persistence	Fast reads from cache, durable writes to disk
Synchronous init loading	Avoids async initialization complexity
Dictionary keyed by ID	O(1) lookups by identifier
Generic over `Codable & Identifiable`	Reusable across any model type
Atomic file writes (`.atomic`)	Prevents partial writes on crash

Best Practices

Use Sendable types for all data crossing actor boundaries
Keep the actor's public API minimal — only expose domain operations, not persistence details
Use .atomic writes to prevent data corruption if the app crashes mid-write
Load synchronously in init — async initializers add complexity with minimal benefit for local files
Combine with @Observable ViewModels for reactive UI updates

Anti-Patterns to Avoid

Using DispatchQueue or NSLock instead of actors for new Swift concurrency code
Exposing the internal cache dictionary to external callers
Making the file URL configurable without validation
Forgetting that all actor method calls are await — callers must handle async context
Using nonisolated to bypass actor isolation (defeats the purpose)

When to Use

Local data storage in iOS/macOS apps (user data, settings, cached content)
Offline-first architectures that sync to a server later
Any shared mutable state that multiple parts of the app access concurrently
Replacing legacy DispatchQueue-based thread safety with modern Swift concurrency

来源与署名

来源：affaan-m/ecc位于.kiro/skills/swift-actor-persistence提交ef648e0

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举报或申请下架

Swift Actor Persistence

Swift Actors for Thread-Safe Persistence

When to Activate

Core Pattern

Actor-Based Repository

Usage

Combining with @Observable ViewModel

Key Design Decisions

Best Practices

Anti-Patterns to Avoid

When to Use

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