Swift Actor Persistence

affaan-m/ECC/docs/zh-CN/skills/swift-actor-persistence

by affaan-mef648e01899ba3e8dc6371642deaaf64b4477775No license275K starsListed Oct 9, 2026Updated Oct 9, 2026Repository updated 4 days ago

在 Swift 中使用 actor 实现线程安全的数据持久化——基于内存缓存与文件支持的存储，通过设计消除数据竞争。

Instructions onlySoftware Development

AI-generated overview

Patterns for building thread-safe Swift data persistence with actors, in-memory caching, and file-backed storage.

What it does: The skill documents a Swift actor-based repository pattern that combines an in-memory dictionary cache with JSON file persistence. It provides generic Codable and Identifiable storage code, usage examples, integration with an @Observable view model, a table of design decisions, best practices, and anti-patterns. The deliverable is guidance and code patterns rather than a runnable tool.
When to use it: Use it when building a data persistence layer in Swift 5.5+ that needs thread-safe access to shared mutable state. It also fits offline-first apps with local storage, or replacing lock- and DispatchQueue-based synchronization with Swift concurrency.
Requirements: Requires Swift 5.5+ and the Swift concurrency model; no scripts, packages, credentials, or network access are included.

用于线程安全持久化的 Swift Actor

使用 Swift actor 构建线程安全数据持久化层的模式。结合内存缓存与文件支持的存储，利用 actor 模型在编译时消除数据竞争。

何时激活

在 Swift 5.5+ 中构建数据持久化层
需要对共享可变状态进行线程安全访问
希望消除手动同步（锁、DispatchQueue）
构建具有本地存储的离线优先应用

核心模式

基于 Actor 的存储库

Actor 模型保证了序列化访问 —— 没有数据竞争，由编译器强制执行。

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(uniqueKeysWithValues: items.map { ($0.id, $0) })    }}

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(uniqueKeysWithValues: items.map { ($0.id, $0) })    }}

用法

由于 actor 隔离，所有调用都会自动变为异步：

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")

与 @Observable ViewModel 结合使用

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()    }}

关键设计决策

决策	理由
Actor（而非类 + 锁）	编译器强制执行的线程安全性，无需手动同步
内存缓存 + 文件持久化	从缓存中快速读取，持久化写入磁盘
同步初始化加载	避免异步初始化的复杂性
按 ID 键控的字典	按标识符进行 O(1) 查找
泛型化 `Codable & Identifiable`	可在任何模型类型中重复使用
原子文件写入 (`.atomic`)	防止崩溃时部分写入

最佳实践

对所有跨越 actor 边界的数据使用 Sendable 类型
保持 actor 的公共 API 最小化 —— 仅暴露领域操作，而非持久化细节
使用 .atomic 写入以防止应用在写入过程中崩溃导致数据损坏
在 init 中同步加载 —— 异步初始化器会增加复杂性，而对本地文件的益处微乎其微
与 @Observable ViewModel 结合使用以实现响应式 UI 更新

应避免的反模式

在 Swift 并发新代码中使用 DispatchQueue 或 NSLock 而非 actor
将内部缓存字典暴露给外部调用者
在不进行验证的情况下使文件 URL 可配置
忘记所有 actor 方法调用都是 await —— 调用者必须处理异步上下文
使用 nonisolated 来绕过 actor 隔离（违背了初衷）

何时使用

iOS/macOS 应用中的本地数据存储（用户数据、设置、缓存内容）
稍后同步到服务器的离线优先架构
应用中多个部分并发访问的任何共享可变状态
用现代 Swift 并发性替换基于 DispatchQueue 的旧式线程安全机制

Source and attribution

Source:affaan-m/ECCindocs/zh-CN/skills/swift-actor-persistenceat commitef648e0

License: No license

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Swift Actor Persistence

用于线程安全持久化的 Swift Actor

何时激活

核心模式

基于 Actor 的存储库

用法

与 @Observable ViewModel 结合使用

关键设计决策

最佳实践

应避免的反模式

何时使用

Source and attribution

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