无法从根提供者解析作用域服务. ASP.NET MVC应用程序App

问题描述

限时删除！！

我正在使用Adam Freeman的Pro ASP.NET Core MVC 6th Edition做商店应用程序.书中的示例是在Core 1.0中制作的，而我正在使用Core 3.0.尝试将数据播种到数据库(entityFramework)时，出现以下错误.

I am doing Store application with Pro ASP.NET Core MVC 6th Edition by Adam Freeman. The example in book is made in Core 1.0, and I am using Core 3.0. I get error as below, while trying to seed data to my database (entityFramework).

下面是我的代码:

 public class SeedData
    {
        public static void EnsurePopulated(IApplicationBuilder app)
        {
            ApplicationDbContext context = app.ApplicationServices.GetRequiredService<ApplicationDbContext>();
            if (!context.Products.Any())
            {
                context.Products.AddRange(
                    new Product {
                        Name = "Witcher",
                        Description = "Geralt the Witcher",
                        Category = "Fantasy",
                        Price = 30 }
                    );
                context.SaveChanges();
            }
        }

启动类:

public class Startup
{
    public IConfiguration Configuration { get; }

    public Startup(IConfiguration configuration, Microsoft.AspNetCore.Hosting.IHostingEnvironment env)
    {
        Configuration = new ConfigurationBuilder().SetBasePath(env.ContentRootPath).AddJsonFile("appsettings.json").Build();
    }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration["Data:BookStoreProducts:ConnectionString"]));
        services.AddTransient<IProductRepository, EFProductRepository>();
        services.AddControllersWithViews();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory, ApplicationDbContext context)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
            app.UseHsts();
        }
        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseRouting();
        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller=Product}/{action=List}/{id?}");
        });
        SeedData.EnsurePopulated(app);
    }
}

和Program.cs

And Program.cs

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

我在依赖注入方面还比较陌生，因此可以对发生的情况进行一些解释.我在网上搜索答案超过两个小时，没有任何结果.

I am rather new in dependency injection so some explanation what is happening would be nice. I am searchin answer online for more than two hours without any result.

有关错误的更多信息:

因此解决方案是:

var scopeeee = app.ApplicationServices.CreateScope();

ApplicationDbContext context = scopeeee.ServiceProvider.GetRequiredService<ApplicationDbContext>();

在确保方法的开头添加.谢谢！

Added at the beggining of EnsurePopulated method. Thanks!

推荐答案

您需要在EnsurePopulated方法中创建范围，然后从该范围中获取实例.

You need to create scope in EnsurePopulated method and then get instance from this scope.

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