ASP.NET Core in Practice

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// 顺序就是请求经过的顺序（管道直通模型）
app.UseExceptionHandler();       // 1. 异常兜底
app.UseHttpsRedirection();
app.UseRouting();               // 2. 路由匹配
app.UseAuthentication();        // 3. 认证（必须先于授权）
app.UseAuthorization();         // 4. 授权
app.UseRateLimiter();           // 5. 限流
app.MapControllers();           // 6. 端点

// 自定义中间件：约定 UseXXX(this IApplicationBuilder)
app.Use(async (ctx, next) => {
    var sw = Stopwatch.StartNew();
    try { await next(); }                   // 交给下一层
    finally {
        logger.LogInformation("{Path} {Status} {Ms}ms",
            ctx.Request.Path, ctx.Response.StatusCode, sw.ElapsedMilliseconds);
    }
});

// 注册：builder.Services.AddXxx
builder.Services.AddSingleton<IClock, SystemClock>();          // 单例：全程一个
builder.Services.AddScoped<IShopDb, ShopDb>();                 // 作用域：每请求一个
builder.Services.AddTransient<IEmailer, SmtpEmailer>();        // 瞬时：每次注入新建

// 构造函数注入（首选）
class OrderService(IShopDb db, IClock clock) {
    public Task CreateAsync(Order o) => db.InsertAsync(o);
}

// 接口多实现：键注册 + 键取
// [FromKeyedServices("fast")] ICache cache

// 依赖关系：注册顺序无关，容器拓扑排序
// 切换实现只需改注册处（mock 测试、A/B 新实现）

Scoped services must not be injected into singletons (captive dependency); inject IServiceProvider and create a scope manually if a background service needs them.

// 最小 API：适合中小项目，一行一个端点
app.MapPost("/orders", async (CreateOrder cmd, IShopDb db, CancellationToken ct) => {
    var order = new Order(cmd.UserId, cmd.Amount);
    await db.InsertAsync(order, ct);
    return Results.Created($"/orders/{order.Id}", order);
})
.WithName("CreateOrder")
.WithOpenApi();

// 控制器：复杂项目分层
[ApiController]
[Route("api/[controller]")]
public class OrdersController(IShopDb db) : ControllerBase {
    [HttpGet("{id}")]
    public async Task<ActionResult<Order>> Get(int id, CancellationToken ct) {
        var o = await db.FindAsync(id, ct);
        return o is null ? NotFound() : Ok(o);
    }
}

// 切换：builder.Services.AddControllers(); app.MapControllers();

builder.Configuration.AddJsonFile("appsettings.json");
builder.Configuration.AddEnvironmentVariables(prefix: "SHOP_");
// 强类型配置
builder.Services.Configure<DbOpt>(builder.Configuration.GetSection("Db"));

var logger = app.Logger;    // 内置结构化日志（可用 Serilog/Seq 接管）
logger.LogInformation("user {Id} created order {OrderId}", uid, oid);

// 健康检查（K8s 探针用）
builder.Services.AddHealthChecks()
    .AddNpgSql(connectionString)
    .AddUrlGroup(new Uri("https://upstream/x"), "upstream");
app.MapHealthChecks("/health");       // /health/ready /health/live 需自行分流

// IHostedService / BackgroundService：常驻任务
class OrderWorker(IShopDb db) : BackgroundService {
    protected override async Task ExecuteAsync(CancellationToken ct) {
        while (!ct.IsCancellationRequested) {
            await SweepExpiredAsync(ct);
            await Task.Delay(TimeSpan.FromMinutes(5), ct);
        }
    }
}
builder.Services.AddHostedService<OrderWorker>();

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// 顺序就是请求经过的顺序（管道直通模型）
app.UseExceptionHandler();       // 1. 异常兜底
app.UseHttpsRedirection();
app.UseRouting();               // 2. 路由匹配
app.UseAuthentication();        // 3. 认证（必须先于授权）
app.UseAuthorization();         // 4. 授权
app.UseRateLimiter();           // 5. 限流
app.MapControllers();           // 6. 端点

// 自定义中间件：约定 UseXXX(this IApplicationBuilder)
app.Use(async (ctx, next) => {
    var sw = Stopwatch.StartNew();
    try { await next(); }                   // 交给下一层
    finally {
        logger.LogInformation("{Path} {Status} {Ms}ms",
            ctx.Request.Path, ctx.Response.StatusCode, sw.ElapsedMilliseconds);
    }
});

// 注册：builder.Services.AddXxx
builder.Services.AddSingleton<IClock, SystemClock>();          // 单例：全程一个
builder.Services.AddScoped<IShopDb, ShopDb>();                 // 作用域：每请求一个
builder.Services.AddTransient<IEmailer, SmtpEmailer>();        // 瞬时：每次注入新建

// 构造函数注入（首选）
class OrderService(IShopDb db, IClock clock) {
    public Task CreateAsync(Order o) => db.InsertAsync(o);
}

// 接口多实现：键注册 + 键取
// [FromKeyedServices("fast")] ICache cache

// 依赖关系：注册顺序无关，容器拓扑排序
// 切换实现只需改注册处（mock 测试、A/B 新实现）

不能把 Scoped 服务注入 Singleton（被俘获依赖）；后台服务需要 Scoped 时注入 IServiceProvider 并手动建作用域。

// 最小 API：适合中小项目，一行一个端点
app.MapPost("/orders", async (CreateOrder cmd, IShopDb db, CancellationToken ct) => {
    var order = new Order(cmd.UserId, cmd.Amount);
    await db.InsertAsync(order, ct);
    return Results.Created($"/orders/{order.Id}", order);
})
.WithName("CreateOrder")
.WithOpenApi();

// 控制器：复杂项目分层
[ApiController]
[Route("api/[controller]")]
public class OrdersController(IShopDb db) : ControllerBase {
    [HttpGet("{id}")]
    public async Task<ActionResult<Order>> Get(int id, CancellationToken ct) {
        var o = await db.FindAsync(id, ct);
        return o is null ? NotFound() : Ok(o);
    }
}

// 切换：builder.Services.AddControllers(); app.MapControllers();

builder.Configuration.AddJsonFile("appsettings.json");
builder.Configuration.AddEnvironmentVariables(prefix: "SHOP_");
// 强类型配置
builder.Services.Configure<DbOpt>(builder.Configuration.GetSection("Db"));

var logger = app.Logger;    // 内置结构化日志（可用 Serilog/Seq 接管）
logger.LogInformation("user {Id} created order {OrderId}", uid, oid);

// 健康检查（K8s 探针用）
builder.Services.AddHealthChecks()
    .AddNpgSql(connectionString)
    .AddUrlGroup(new Uri("https://upstream/x"), "upstream");
app.MapHealthChecks("/health");       // /health/ready /health/live 需自行分流

// IHostedService / BackgroundService：常驻任务
class OrderWorker(IShopDb db) : BackgroundService {
    protected override async Task ExecuteAsync(CancellationToken ct) {
        while (!ct.IsCancellationRequested) {
            await SweepExpiredAsync(ct);
            await Task.Delay(TimeSpan.FromMinutes(5), ct);
        }
    }
}
builder.Services.AddHostedService<OrderWorker>();