ASP.NET Core 6 如何在启动期间访问配置

Question

在早期版本中，我们有 Startup.cs 类，我们在 Startup 文件中获取配置对象如下。

public class Startup 
{
    private readonly IHostEnvironment environment;
    private readonly IConfiguration config;

    public Startup(IConfiguration configuration, IHostEnvironment environment) 
    {
        this.config = configuration;
        this.environment = environment;
    }

    public void ConfigureServices(IServiceCollection services) 
    {
        // Add Services
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env) 
    {
        // Add Middlewares
    }

}

---

现在在 .NET 6（使用 Visual Studio 2022）中，我们看不到 Startup.cs 类。看起来它的日子已经屈指可数了。那么我们如何获取Configuration(IConfiguration)和Hosting Environment(IHostEnvironment)这样的对象

我们如何获取这些对象，比如从 appsettings 中读取配置？目前 Program.cs 文件如下所示。

using Festify.Database;
using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();

builder.Services.AddDbContext<FestifyContext>();


////////////////////////////////////////////////
// The following is Giving me error as Configuration 
// object is not avaible, I dont know how to inject this here.
////////////////////////////////////////////////


builder.Services.AddDbContext<FestifyContext>(opt =>
        opt.UseSqlServer(
            Configuration.GetConnectionString("Festify")));


var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

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

app.UseRouting();

app.UseAuthorization();

app.MapRazorPages();

app.Run();

我想知道如何从 appsettings.json 中读取配置？

Answer 1

WebApplication.CreateBuilder(args) 返回的WebApplicationBuilder 暴露了Configuration 和Environment 属性：

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
...
ConfigurationManager configuration = builder.Configuration;
IWebHostEnvironment environment = builder.Environment;

WebApplicationBuilder.Build() 返回的WebApplication 也暴露了Configuration 和Environment：

var app = builder.Build();
IConfiguration configuration = app.Configuration;
IWebHostEnvironment environment = app.Environment;

还要检查migration guide 和code samples。

Answer 2

在Program.cs 中，WebApplicationBuilder 创建如下所示。

var builder = WebApplication.CreateBuilder(args);

一旦我们创建了构建器，配置就可用了。

假设您有默认的appSettings.json。下面的示例代码将从 JSON 配置文件返回配置默认日志级别设置。

builder.Configuration["Logging:LogLevel:Default"] // returns "Warning"

应用运行后，您可以在应用的其他类中通过依赖注入访问配置设置。

public MyClass(IConfiguration configuration)
{
   var logLevel = configuration["Logging:LogLevel:Default"];
}

一个值得考虑的好功能是创建一个代表您的设置的类，然后将配置绑定到该类类型的实例。例如，假设您创建了一个名为 MyAppSettings 的新类，其结构与您的 appSettings.json 相同，您可以执行以下操作：

var myAppSettings = builder.Configuration.Get<MyAppSettings>();
string logLevel = myAppSettings.Logging.LogLevel.Default;

Answer 3

您只需要添加“builder”。在您的配置之前

喜欢：

builder.Services.AddDbContext<FestifyContext>(opt =>opt.UseSqlServer(builder.Configuration.GetConnectionString("Festify")));

Answer 4

以下代码对我有用：

程序.cs：

var builder = WebApplication.CreateBuilder(args);
string connString = builder.Configuration.GetConnectionString("conStr");
ConnectionString = connString;

...

partial class Program
{
    public static string? ConnectionString { get; private set; }
}

calling class:
string cnStr = Program.ConnectionString;

Answer 5

这对我有用 ---

// Read in from JSON file
builder.Services.Configure<ConnectionKeys>(builder.Configuration.GetSection("ConnectionKeys"));

Answer 6

.NET 6 已经在 Program.cs 中提供了构建器对象

var builder = WebApplication.CreateBuilder(args);

以该builder访问配置和Environment为例，从app.settings.cs获取ConnectionString如下：

builder.Services.AddDbContext<DataContext>( options =>
{
  options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnectiion"));
});