无法从根提供者解析作用域服务. ASP.NET MVC应用程序App [英] Cannot resolve scoped service from root provider. ASP.NET MVC app App

问题描述

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).

System.InvalidOperationException:'无法解析作用域服务 根提供商提供的"BookStore.Models.ApplicationDbContext".

System.InvalidOperationException: 'Cannot resolve scoped service 'BookStore.Models.ApplicationDbContext' from root provider.'

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:

在 Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteValidator.ValidateResolution(Type serviceType，IServiceScope范围，IServiceScope rootScope)位于 Microsoft.Extensions.DependencyInjection.ServiceProvider.Microsoft.Extensions.DependencyInjection.ServiceLookup.IServiceProviderEngineCallback.OnResolve(Type serviceType，IServiceScope范围)，位于 Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType，ServiceProviderEngineScope serviceProviderEngineScope)
在 Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)在 Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider 提供者，键入serviceType)，位于 Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService [T](IServiceProvider 供应商) BookStore.Models.SeedData.EnsurePopulated(IApplicationBuilder app)在 C:\ Users \ Piotr \ source \ repos \ Store \ BookStore \ Models \ SeedData.cs:第12行 在BookStore.Startup.Configure(IApplicationBuilder应用， IWebHostEnvironment env，ILoggerFactory loggerFactory， ApplicationDbContext上下文)中 C:\ Users \ Piotr \ source \ repos \ Store \ BookStore \ Startup.cs:第51行位于 System.RuntimeMethodHandle.InvokeMethod(对象目标，对象[] 参数，签名sig，布尔构造函数，布尔wrapExceptions) 在System.Reflection.RuntimeMethodInfo.Invoke(Object obj，BindingFlags invokeAttr，活页夹活页夹，Object []参数，CultureInfo文化)
在Microsoft.AspNetCore.Hosting.ConfigureBuilder.Invoke(Object 例如IApplicationBuilder构建器) Microsoft.AspNetCore.Hosting.ConfigureBuilder.<> c__DisplayClass4_0.b__0(IApplicationBuilder 建造者) Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<> c__DisplayClass13_0.b__2(IApplicationBuilder 应用程式) Microsoft.AspNetCore.Mvc.Filters.MiddlewareFilterBuilderStartupFilter.<> c__DisplayClass0_0.g__MiddlewareFilterBuilder | 0(IApplicationBuilder 建造者) Microsoft.AspNetCore.Server.IIS.Core.IISServerSetupFilter.<> c__DisplayClass2_0.b__0(IApplicationBuilder 应用程式) Microsoft.AspNetCore.HostFilteringStartupFilter.<> c__DisplayClass0_0.b__0(IApplicationBuilder 应用程式) Microsoft.AspNetCore.Hosting.GenericWebHostService.d__31.MoveNext()

at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteValidator.ValidateResolution(Type serviceType, IServiceScope scope, IServiceScope rootScope) at Microsoft.Extensions.DependencyInjection.ServiceProvider.Microsoft.Extensions.DependencyInjection.ServiceLookup.IServiceProviderEngineCallback.OnResolve(Type serviceType, IServiceScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at BookStore.Models.SeedData.EnsurePopulated(IApplicationBuilder app) in C:\Users\Piotr\source\repos\Store\BookStore\Models\SeedData.cs:line 12 at BookStore.Startup.Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory, ApplicationDbContext context) in C:\Users\Piotr\source\repos\Store\BookStore\Startup.cs:line 51 at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor, Boolean wrapExceptions) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Microsoft.AspNetCore.Hosting.ConfigureBuilder.Invoke(Object instance, IApplicationBuilder builder) at Microsoft.AspNetCore.Hosting.ConfigureBuilder.<>c__DisplayClass4_0.b__0(IApplicationBuilder builder) at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>c__DisplayClass13_0.b__2(IApplicationBuilder app) at Microsoft.AspNetCore.Mvc.Filters.MiddlewareFilterBuilderStartupFilter.<>c__DisplayClass0_0.g__MiddlewareFilterBuilder|0(IApplicationBuilder builder) at Microsoft.AspNetCore.Server.IIS.Core.IISServerSetupFilter.<>c__DisplayClass2_0.b__0(IApplicationBuilder app) at Microsoft.AspNetCore.HostFilteringStartupFilter.<>c__DisplayClass0_0.b__0(IApplicationBuilder app) at Microsoft.AspNetCore.Hosting.GenericWebHostService.d__31.MoveNext()

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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