ASP.NET Core 5 MVC中ConfigureServices与Startup类去向问题

这是ASP.NET Core 5引入的最小托管模型，微软对项目启动流程做了简化，把原Startup类里的两部分核心逻辑直接整合到了Program.cs的Main方法中：

原 ConfigureServices 方法的替代 #

原ConfigureServices中注册服务的逻辑，现在通过WebApplication.CreateBuilder(args)返回的builder.Services来实现。你代码里的这些部分就是对应原ConfigureServices的功能：

// Add services to the container.
var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
    .AddEntityFrameworkStores<ApplicationDbContext>();
builder.Services.AddRazorPages();

原 Configure 方法的替代 #

原Configure中配置HTTP请求管道的逻辑，现在在builder.Build()得到app实例后执行。你代码里的这些部分对应原Configure的功能：

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseMigrationsEndPoint();
}
else
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthentication();
app.UseAuthorization();

app.MapRazorPages();

如果偏好传统的Startup类结构，你可以手动创建Startup类并保留ConfigureServices和Configure方法，然后在Program.cs中修改为：

var builder = WebApplication.CreateBuilder(args);
builder.UseStartup<Startup>();
var app = builder.Build();
app.Run();

你的完整启动代码如下：

public class Program
{
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);
            
            // Add services to the container.
            var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");
            builder.Services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(connectionString));
            builder.Services.AddDatabaseDeveloperPageExceptionFilter();

            builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
                .AddEntityFrameworkStores<ApplicationDbContext>();
            builder.Services.AddRazorPages();

            var app = builder.Build();

            // Configure the HTTP request pipeline.
            if (app.Environment.IsDevelopment())
            {
                app.UseMigrationsEndPoint();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthentication();
            app.UseAuthorization();

            app.MapRazorPages();

            app.Run();
        }
}

内容的提问来源于stack exchange，提问作者Yoda