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.NET Development Patterns

.NET开发模式

Idiomatic C# and .NET patterns for building robust, performant, and maintainable applications.
用于构建健壮、高性能、可维护应用的地道C#与.NET开发模式。

When to Activate

适用场景

  • Writing new C# code
  • Reviewing C# code
  • Refactoring existing .NET applications
  • Designing service architectures with ASP.NET Core
  • 编写新的C#代码时
  • 评审C#代码时
  • 重构现有.NET应用时
  • 使用ASP.NET Core设计服务架构时

Core Principles

核心原则

1. Prefer Immutability

1. 优先使用不可变性

Use records and init-only properties for data models. Mutability should be an explicit, justified choice.
csharp
// Good: Immutable value object
public sealed record Money(decimal Amount, string Currency);

// Good: Immutable DTO with init setters
public sealed class CreateOrderRequest
{
    public required string CustomerId { get; init; }
    public required IReadOnlyList<OrderItem> Items { get; init; }
}

// Bad: Mutable model with public setters
public class Order
{
    public string CustomerId { get; set; }
    public List<OrderItem> Items { get; set; }
}
数据模型使用records和init-only属性，仅在有明确合理理由时才使用可变性。
csharp
// Good: Immutable value object
public sealed record Money(decimal Amount, string Currency);

// Good: Immutable DTO with init setters
public sealed class CreateOrderRequest
{
    public required string CustomerId { get; init; }
    public required IReadOnlyList<OrderItem> Items { get; init; }
}

// Bad: Mutable model with public setters
public class Order
{
    public string CustomerId { get; set; }
    public List<OrderItem> Items { get; set; }
}

2. Explicit Over Implicit

2. 显式优于隐式

Be clear about nullability, access modifiers, and intent.
csharp
// Good: Explicit access modifiers and nullability
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);
    }
}
明确可空性、访问修饰符和代码意图。
csharp
// Good: Explicit access modifiers and nullability
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. Depend on Abstractions

3. 依赖抽象

Use interfaces for service boundaries. Register via DI container.
csharp
// Good: Interface-based dependency
public interface IOrderRepository
{
    Task<Order?> FindByIdAsync(Guid id, CancellationToken cancellationToken);
    Task<IReadOnlyList<Order>> FindByCustomerAsync(string customerId, CancellationToken cancellationToken);
    Task AddAsync(Order order, CancellationToken cancellationToken);
}

// Registration
builder.Services.AddScoped<IOrderRepository, SqlOrderRepository>();
服务边界使用接口定义，通过DI容器注册。
csharp
// Good: Interface-based dependency
public interface IOrderRepository
{
    Task<Order?> FindByIdAsync(Guid id, CancellationToken cancellationToken);
    Task<IReadOnlyList<Order>> FindByCustomerAsync(string customerId, CancellationToken cancellationToken);
    Task AddAsync(Order order, CancellationToken cancellationToken);
}

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

Async/Await Patterns

Async/Await模式

Proper Async Usage

正确的Async用法

csharp
// Good: Async all the way, with CancellationToken
public async Task<OrderSummary> GetOrderSummaryAsync(
    Guid orderId,
    CancellationToken cancellationToken)
{
    var order = await _repository.FindByIdAsync(orderId, cancellationToken)
        ?? throw new NotFoundException($"Order {orderId} not found");

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

    return new OrderSummary(order, customer);
}

// Bad: Blocking on async
public OrderSummary GetOrderSummary(Guid orderId)
{
    var order = _repository.FindByIdAsync(orderId, CancellationToken.None).Result; // Deadlock risk
    return new OrderSummary(order);
}
csharp
// Good: Async all the way, with CancellationToken
public async Task<OrderSummary> GetOrderSummaryAsync(
    Guid orderId,
    CancellationToken cancellationToken)
{
    var order = await _repository.FindByIdAsync(orderId, cancellationToken)
        ?? throw new NotFoundException($"Order {orderId} not found");

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

    return new OrderSummary(order, customer);
}

// Bad: Blocking on async
public OrderSummary GetOrderSummary(Guid orderId)
{
    var order = _repository.FindByIdAsync(orderId, CancellationToken.None).Result; // Deadlock risk
    return new OrderSummary(order);
}

Parallel Async Operations

并行异步操作

csharp
// Good: Concurrent independent operations
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);
}
csharp
// Good: Concurrent independent operations
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 Pattern

选项模式

Bind configuration sections to strongly-typed objects.
csharp
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;
}

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

// Usage via injection
public class EmailService(IOptions<SmtpOptions> options)
{
    private readonly SmtpOptions _smtp = options.Value;
}
将配置节绑定到强类型对象。
csharp
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;
}

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

// Usage via injection
public class EmailService(IOptions<SmtpOptions> options)
{
    private readonly SmtpOptions _smtp = options.Value;
}

Result Pattern

结果模式

Return explicit success/failure instead of throwing for expected failures.
csharp
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);
}

// Usage
public async Task<Result<Order>> PlaceOrderAsync(CreateOrderRequest request)
{
    if (request.Items.Count == 0)
        return Result<Order>.Failure("Order must contain at least one item");

    var order = Order.Create(request);
    await _repository.AddAsync(order, CancellationToken.None);
    return Result<Order>.Success(order);
}
对预期内的失败返回明确的成功/失败状态，而非抛出异常。
csharp
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);
}

// Usage
public async Task<Result<Order>> PlaceOrderAsync(CreateOrderRequest request)
{
    if (request.Items.Count == 0)
        return Result<Order>.Failure("Order must contain at least one item");

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

Repository Pattern with EF Core

搭配EF Core的仓储模式

csharp
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);
    }
}
csharp
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);
    }
}

Middleware and Pipeline

中间件与管道

csharp
// Custom middleware
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(
                "Request {Method} {Path} completed in {ElapsedMs}ms with status {StatusCode}",
                context.Request.Method,
                context.Request.Path,
                stopwatch.ElapsedMilliseconds,
                context.Response.StatusCode);
        }
    }
}
csharp
// Custom middleware
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(
                "Request {Method} {Path} completed in {ElapsedMs}ms with status {StatusCode}",
                context.Request.Method,
                context.Request.Path,
                stopwatch.ElapsedMilliseconds,
                context.Response.StatusCode);
        }
    }
}

Minimal API Patterns

极简API模式

csharp
// Organized with route groups
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);
});
csharp
// Organized with route groups
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);
});

Guard Clauses

卫语句

csharp
// Good: Early returns with clear validation
public async Task<ProcessResult> ProcessPaymentAsync(
    PaymentRequest request,
    CancellationToken cancellationToken)
{
    ArgumentNullException.ThrowIfNull(request);

    if (request.Amount <= 0)
        throw new ArgumentOutOfRangeException(nameof(request.Amount), "Amount must be positive");

    if (string.IsNullOrWhiteSpace(request.Currency))
        throw new ArgumentException("Currency is required", nameof(request.Currency));

    // Happy path continues here without nesting
    var gateway = _gatewayFactory.Create(request.Currency);
    return await gateway.ChargeAsync(request, cancellationToken);
}
csharp
// Good: Early returns with clear validation
public async Task<ProcessResult> ProcessPaymentAsync(
    PaymentRequest request,
    CancellationToken cancellationToken)
{
    ArgumentNullException.ThrowIfNull(request);

    if (request.Amount <= 0)
        throw new ArgumentOutOfRangeException(nameof(request.Amount), "Amount must be positive");

    if (string.IsNullOrWhiteSpace(request.Currency))
        throw new ArgumentException("Currency is required", nameof(request.Currency));

    // Happy path continues here without nesting
    var gateway = _gatewayFactory.Create(request.Currency);
    return await gateway.ChargeAsync(request, cancellationToken);
}

Anti-Patterns to Avoid

需要避免的反模式

Anti-PatternFix
async void
methods		Return 
Task
(except event handlers)
.Result
or 
.Wait()
Use 
await
catch (Exception) { }
Handle or rethrow with context
new Service()
in constructors		Use constructor injection
public
fields		Use properties with appropriate accessors
dynamic
in business logic		Use generics or explicit types
Mutable 
static
state		Use DI scoping or 
ConcurrentDictionary
string.Format
in loops		Use 
StringBuilder
or interpolated string handlers
反模式解决方案
async void
methods		返回
Task
（事件处理程序除外）
.Result
or 
.Wait()
使用
await
catch (Exception) { }
处理异常或携带上下文重新抛出
new Service()
in constructors		使用构造函数注入
public
fields		使用带合适访问器的属性
dynamic
in business logic		使用泛型或显式类型
Mutable 
static
state		使用DI作用域或
ConcurrentDictionary
string.Format
in loops		使用
StringBuilder
或插值字符串处理器