dotnet-patterns

.NET 开发模式

地道的 C# 和 .NET 模式，用于构建健壮、高性能和可维护的应用程序。

何时激活

• 编写新的 C# 代码
• 审查 C# 代码
• 重构现有 .NET 应用程序
• 使用 ASP.NET Core 设计服务架构

核心原则

1. 优先不可变性

对数据模型使用 record 和 init-only 属性。可变性应该是显式的、有理由的选择。

// 好：不可变的值对象
public sealed record Money(decimal Amount, string Currency);

// 好：带 init setter 的不可变 DTO
public sealed class CreateOrderRequest
{
    public required string CustomerId { get; init; }
    public required IReadOnlyList<OrderItem> Items { get; init; }
}

// 差：带公共 setter 的可变模型
public class Order
{
    public string CustomerId { get; set; }
    public List<OrderItem> Items { get; set; }
}

2. 显式优于隐式

明确表达可空性、访问修饰符和意图。

// 好：显式的访问修饰符和可空性
public sealed class UserService
{
    private readonly IUserRepository _repository;
    private readonly ILogger<UserService> _logger;

    public UserService(IUserRepository repository, ILogger<UserService> logger)
    {
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<User?> FindByIdAsync(Guid id, CancellationToken cancellationToken)
    {
        return await _repository.FindByIdAsync(id, cancellationToken);
    }
}

3. 依赖抽象

在服务边界使用接口。通过 DI 容器注册。

// 好：基于接口的依赖
public interface IOrderRepository
{
    Task<Order?> FindByIdAsync(Guid id, CancellationToken cancellationToken);
    Task<IReadOnlyList<Order>> FindByCustomerAsync(string customerId, CancellationToken cancellationToken);
    Task AddAsync(Order order, CancellationToken cancellationToken);
}

// 注册
builder.Services.AddScoped<IOrderRepository, SqlOrderRepository>();

Async/Await 模式

正确的异步使用

// 好：全程异步，带 CancellationToken
public async Task<OrderSummary> GetOrderSummaryAsync(
    Guid orderId,
    CancellationToken cancellationToken)
{
    var order = await _repository.FindByIdAsync(orderId, cancellationToken)
        ?? throw new NotFoundException($"订单 {orderId} 未找到");

    var customer = await _customerService.GetAsync(order.CustomerId, cancellationToken);

    return new OrderSummary(order, customer);
}

// 差：在异步上阻塞
public OrderSummary GetOrderSummary(Guid orderId)
{
    var order = _repository.FindByIdAsync(orderId, CancellationToken.None).Result; // 死锁风险
    return new OrderSummary(order);
}

并行异步操作

// 好：并发的独立操作
public async Task<DashboardData> LoadDashboardAsync(CancellationToken cancellationToken)
{
    var ordersTask = _orderService.GetRecentAsync(cancellationToken);
    var metricsTask = _metricsService.GetCurrentAsync(cancellationToken);
    var alertsTask = _alertService.GetActiveAsync(cancellationToken);

    await Task.WhenAll(ordersTask, metricsTask, alertsTask);

    return new DashboardData(
        Orders: await ordersTask,
        Metrics: await metricsTask,
        Alerts: await alertsTask);
}

Options 模式

将配置节绑定到强类型对象。

public sealed class SmtpOptions
{
    public const string SectionName = "Smtp";

    public required string Host { get; init; }
    public required int Port { get; init; }
    public required string Username { get; init; }
    public bool UseSsl { get; init; } = true;
}

// 注册
builder.Services.Configure<SmtpOptions>(
    builder.Configuration.GetSection(SmtpOptions.SectionName));

// 通过注入使用
public class EmailService(IOptions<SmtpOptions> options)
{
    private readonly SmtpOptions _smtp = options.Value;
}

Result 模式

返回显式的成功/失败，而非为预期失败抛出异常。

public sealed record Result<T>
{
    public bool IsSuccess { get; }
    public T? Value { get; }
    public string? Error { get; }

    private Result(T value) { IsSuccess = true; Value = value; }
    private Result(string error) { IsSuccess = false; Error = error; }

    public static Result<T> Success(T value) => new(value);
    public static Result<T> Failure(string error) => new(error);
}

// 使用
public async Task<Result<Order>> PlaceOrderAsync(CreateOrderRequest request)
{
    if (request.Items.Count == 0)
        return Result<Order>.Failure("订单必须包含至少一个商品");

    var order = Order.Create(request);
    await _repository.AddAsync(order, CancellationToken.None);
    return Result<Order>.Success(order);
}

使用 EF Core 的仓储模式

public sealed class SqlOrderRepository : IOrderRepository
{
    private readonly AppDbContext _db;

    public SqlOrderRepository(AppDbContext db) => _db = db;

    public async Task<Order?> FindByIdAsync(Guid id, CancellationToken cancellationToken)
    {
        return await _db.Orders
            .Include(o => o.Items)
            .AsNoTracking()
            .FirstOrDefaultAsync(o => o.Id == id, cancellationToken);
    }

    public async Task<IReadOnlyList<Order>> FindByCustomerAsync(
        string customerId,
        CancellationToken cancellationToken)
    {
        return await _db.Orders
            .Where(o => o.CustomerId == customerId)
            .OrderByDescending(o => o.CreatedAt)
            .AsNoTracking()
            .ToListAsync(cancellationToken);
    }

    public async Task AddAsync(Order order, CancellationToken cancellationToken)
    {
        _db.Orders.Add(order);
        await _db.SaveChangesAsync(cancellationToken);
    }
}

中间件和管道

// 自定义中间件
public sealed class RequestTimingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestTimingMiddleware> _logger;

    public RequestTimingMiddleware(RequestDelegate next, ILogger<RequestTimingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var stopwatch = Stopwatch.StartNew();
        try
        {
            await _next(context);
        }
        finally
        {
            stopwatch.Stop();
            _logger.LogInformation(
                "请求 {Method} {Path} 在 {ElapsedMs}ms 内完成，状态 {StatusCode}",
                context.Request.Method,
                context.Request.Path,
                stopwatch.ElapsedMilliseconds,
                context.Response.StatusCode);
        }
    }
}

Minimal API 模式

// 使用路由组组织
var orders = app.MapGroup("/api/orders")
    .RequireAuthorization()
    .WithTags("Orders");

orders.MapGet("/{id:guid}", async (
    Guid id,
    IOrderRepository repository,
    CancellationToken cancellationToken) =>
{
    var order = await repository.FindByIdAsync(id, cancellationToken);
    return order is not null
        ? TypedResults.Ok(order)
        : TypedResults.NotFound();
});

orders.MapPost("/", async (
    CreateOrderRequest request,
    IOrderService service,
    CancellationToken cancellationToken) =>
{
    var result = await service.PlaceOrderAsync(request, cancellationToken);
    return result.IsSuccess
        ? TypedResults.Created($"/api/orders/{result.Value!.Id}", result.Value)
        : TypedResults.BadRequest(result.Error);
});

守卫子句

// 好：早期返回配清晰验证
public async Task<ProcessResult> ProcessPaymentAsync(
    PaymentRequest request,
    CancellationToken cancellationToken)
{
    ArgumentNullException.ThrowIfNull(request);

    if (request.Amount <= 0)
        throw new ArgumentOutOfRangeException(nameof(request.Amount), "金额必须为正数");

    if (string.IsNullOrWhiteSpace(request.Currency))
        throw new ArgumentException("币种是必填项", nameof(request.Currency));

    // 快乐路径在此继续，无嵌套
    var gateway = _gatewayFactory.Create(request.Currency);
    return await gateway.ChargeAsync(request, cancellationToken);
}

需要避免的反模式

反模式	修复
async void 方法	返回 Task（事件处理器除外）
.Result 或 .Wait()	使用 await
catch (Exception) { }	处理或带上下文重新抛出
构造函数中 new Service()	使用构造函数注入
public 字段	使用带适当访问器的属性
业务逻辑中的 dynamic	使用泛型或显式类型
可变的 static 状态	使用 DI 作用域或 ConcurrentDictionary
循环中的 string.Format	使用 StringBuilder 或插值字符串处理器