访问 Microsoft.Extensions.Hosting 服务时出错。未找到应用服务提供者答案

【问题标题】：An error occurred while accessing the Microsoft.Extensions.Hosting services. No application service provider was found访问 Microsoft.Extensions.Hosting 服务时出错。未找到应用服务提供者
【发布时间】：2021-03-24 05:12:57
【问题描述】：

我正在尝试在 Azure DevOps CI 管道中编写/导出 Entity Framework Core 代码优先迁移，但出现错误。下面的命令在我的本地 Visual Studio 中运行良好并生成一个 sql 文件，几个月前该命令在 DevOps 中也运行良好（不确定是否与更新相关）。

dotnet ef migrations script --project Booking.Core 
       --startup-project Booking.Management --idempotent 
       --output $(build.artifactstagingdirectory)/migrate.sql --verbose

我的项目正在使用 .NET Core 3.1.5 版本，并且在管道中我确保 dotnet-ef 命令可用，如

dotnet tool install --global dotnet-ef --version 3.1.5

但我仍然不断收到此错误：

2020-12-13T09:13:27.8973893Z ##[section]Starting: EF Core Migrations SQL Export
2020-12-13T09:13:27.9112206Z ==============================================================================
2020-12-13T09:13:27.9112480Z Task         : PowerShell
2020-12-13T09:13:27.9112737Z Description  : Run a PowerShell script on Linux, macOS, or Windows
2020-12-13T09:13:27.9112956Z Version      : 2.179.1
2020-12-13T09:13:27.9113144Z Author       : Microsoft Corporation
2020-12-13T09:13:27.9113446Z Help         : https://docs.microsoft.com/azure/devops/pipelines/tasks/utility/powershell
2020-12-13T09:13:27.9113759Z ==============================================================================
2020-12-13T09:13:28.8144250Z Generating script.
2020-12-13T09:13:28.8694723Z ========================== Starting Command Output ===========================
2020-12-13T09:13:28.8987598Z ##[command]"C:\windows\System32\WindowsPowerShell\v1.0\powershell.exe" -NoLogo -NoProfile -NonInteractive -ExecutionPolicy Unrestricted -Command ". 'D:\a\_temp\fa82967e-1e57-4dba-932d-1453e98ef510.ps1'"
2020-12-13T09:13:29.4639310Z Using project 'Booking.Core\Booking.Core.csproj'.
2020-12-13T09:13:29.4640261Z Using startup project 'Booking.Management\Booking.Management.csproj'.
2020-12-13T09:13:29.4661731Z Writing 'Booking.Core\obj\Booking.Core.csproj.EntityFrameworkCore.targets'...
2020-12-13T09:13:29.4713085Z dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=C:\Users\VssAdministrator\AppData\Local\Temp\tmpBC2B.tmp /verbosity:quiet /nologo Booking.Core\Booking.Core.csproj
2020-12-13T09:13:30.5894726Z Writing 'Booking.Management\obj\Booking.Management.csproj.EntityFrameworkCore.targets'...
2020-12-13T09:13:30.5904170Z dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=C:\Users\VssAdministrator\AppData\Local\Temp\tmpC091.tmp /verbosity:quiet /nologo Booking.Management\Booking.Management.csproj
2020-12-13T09:13:31.4844212Z Build started...
2020-12-13T09:13:31.4848105Z dotnet build Booking.Management\Booking.Management.csproj /verbosity:quiet /nologo
2020-12-13T09:13:39.4566730Z 
2020-12-13T09:13:39.4680169Z Build succeeded.
2020-12-13T09:13:39.4681347Z     0 Warning(s)
2020-12-13T09:13:39.4681964Z     0 Error(s)
2020-12-13T09:13:39.4682460Z 
2020-12-13T09:13:39.4683029Z Time Elapsed 00:00:07.53
2020-12-13T09:13:39.5195940Z Build succeeded.
2020-12-13T09:13:39.5465861Z dotnet exec --depsfile D:\a\1\s\Booking.Management\bin\Debug\netcoreapp3.1\Booking.Management.deps.json --additionalprobingpath C:\Users\VssAdministrator\.nuget\packages --additionalprobingpath "C:\Program Files\dotnet\sdk\NuGetFallbackFolder" --runtimeconfig D:\a\1\s\Booking.Management\bin\Debug\netcoreapp3.1\Booking.Management.runtimeconfig.json C:\Users\VssAdministrator\.dotnet\tools\.store\dotnet-ef\3.1.5\dotnet-ef\3.1.5\tools\netcoreapp3.1\any\tools\netcoreapp2.0\any\ef.dll migrations script --idempotent --output D:\a\1\a/migrate.sql --assembly D:\a\1\s\Booking.Management\bin\Debug\netcoreapp3.1\Booking.Core.dll --startup-assembly D:\a\1\s\Booking.Management\bin\Debug\netcoreapp3.1\Booking.Management.dll --project-dir D:\a\1\s\Booking.Core\ --language C# --working-dir D:\a\1\s --verbose --root-namespace Booking.Core
2020-12-13T09:13:39.7619178Z Using assembly 'Booking.Core'.
2020-12-13T09:13:39.7621486Z Using startup assembly 'Booking.Management'.
2020-12-13T09:13:39.7623162Z Using application base 'D:\a\1\s\Booking.Management\bin\Debug\netcoreapp3.1'.
2020-12-13T09:13:39.7624489Z Using working directory 'D:\a\1\s\Booking.Management'.
2020-12-13T09:13:39.7627735Z Using root namespace 'Booking.Core'.
2020-12-13T09:13:39.7628656Z Using project directory 'D:\a\1\s\Booking.Core\'.
2020-12-13T09:13:40.0447318Z Finding DbContext classes...
2020-12-13T09:13:40.0448237Z Finding IDesignTimeDbContextFactory implementations...
2020-12-13T09:13:40.1345335Z Finding application service provider...
2020-12-13T09:13:40.1352141Z Finding Microsoft.Extensions.Hosting service provider...
2020-12-13T09:13:40.1387349Z Using environment 'Development'.
2020-12-13T09:13:41.3123215Z Rollbar.RollbarException: Failed to configure using invalid configuration prototype!
2020-12-13T09:13:41.3123976Z    at Rollbar.RollbarLogger.ValidateConfiguration(IRollbarConfig rollbarConfig)
2020-12-13T09:13:41.3124504Z    at Rollbar.RollbarLogger.Configure(IRollbarConfig settings)
2020-12-13T09:13:41.3125776Z    at Rollbar.RollbarLogger.Rollbar.IRollbar.Configure(IRollbarConfig settings)
2020-12-13T09:13:41.3127983Z    at Booking.Management.Startup.ConfigureServices(IServiceCollection services) in D:\a\1\s\Booking.Management\Startup.cs:line 136
2020-12-13T09:13:41.3128521Z    at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor, Boolean wrapExceptions)
2020-12-13T09:13:41.3129014Z    at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
2020-12-13T09:13:41.3129472Z    at Microsoft.AspNetCore.Hosting.ConfigureServicesBuilder.InvokeCore(Object instance, IServiceCollection services)
2020-12-13T09:13:41.3129921Z    at Microsoft.AspNetCore.Hosting.ConfigureServicesBuilder.<>c__DisplayClass9_0.<Invoke>g__Startup|0(IServiceCollection serviceCollection)
2020-12-13T09:13:41.3130590Z    at Microsoft.AspNetCore.Hosting.ConfigureServicesBuilder.Invoke(Object instance, IServiceCollection services)
2020-12-13T09:13:41.3131087Z    at Microsoft.AspNetCore.Hosting.ConfigureServicesBuilder.<>c__DisplayClass8_0.<Build>b__0(IServiceCollection services)
2020-12-13T09:13:41.3131685Z    at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.UseStartup(Type startupType, HostBuilderContext context, IServiceCollection services)
2020-12-13T09:13:41.3132193Z    at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>c__DisplayClass12_0.<UseStartup>b__0(HostBuilderContext context, IServiceCollection services)
2020-12-13T09:13:41.3132570Z    at Microsoft.Extensions.Hosting.HostBuilder.CreateServiceProvider()
2020-12-13T09:13:41.3132842Z    at Microsoft.Extensions.Hosting.HostBuilder.Build()
2020-12-13T09:13:41.3133338Z An error occurred while accessing the Microsoft.Extensions.Hosting services. Continuing without the application service provider. Error: Failed to configure using invalid configuration prototype!
2020-12-13T09:13:41.3133808Z No application service provider was found.
2020-12-13T09:13:41.3309579Z Finding DbContext classes in the project...
2020-12-13T09:13:41.3402462Z Found DbContext 'ApplicationDbContext'.
2020-12-13T09:13:41.3673060Z Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'ApplicationDbContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
2020-12-13T09:13:41.3674225Z  ---> System.MissingMethodException: No parameterless constructor defined for type 'Booking.Core.Data.ApplicationDbContext'.
2020-12-13T09:13:41.3674932Z    at System.RuntimeType.CreateInstanceDefaultCtorSlow(Boolean publicOnly, Boolean wrapExceptions, Boolean fillCache)
2020-12-13T09:13:41.3675640Z    at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, Boolean wrapExceptions)
2020-12-13T09:13:41.3676267Z    at System.Activator.CreateInstance(Type type, Boolean nonPublic, Boolean wrapExceptions)
2020-12-13T09:13:41.3676691Z    at System.Activator.CreateInstance(Type type)
2020-12-13T09:13:41.3677358Z    at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_3.<FindContextTypes>b__13()
2020-12-13T09:13:41.3677798Z    --- End of inner exception stack trace ---
2020-12-13T09:13:41.3678247Z    at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_3.<FindContextTypes>b__13()
2020-12-13T09:13:41.3678609Z    at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
2020-12-13T09:13:41.3678993Z    at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
2020-12-13T09:13:41.3681847Z    at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.ScriptMigration(String fromMigration, String toMigration, Boolean idempotent, String contextType)
2020-12-13T09:13:41.3682773Z    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScriptMigrationImpl(String fromMigration, String toMigration, Boolean idempotent, String contextType)
2020-12-13T09:13:41.3683262Z    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScriptMigration.<>c__DisplayClass0_0.<.ctor>b__0()
2020-12-13T09:13:41.3683647Z    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
2020-12-13T09:13:41.3684014Z    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
2020-12-13T09:13:41.3684531Z Unable to create an object of type 'ApplicationDbContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
2020-12-13T09:13:41.6277035Z ##[error]PowerShell exited with code '1'.
2020-12-13T09:13:41.6727543Z ##[section]Finishing: EF Core Migrations SQL Export

我的Program.cs 文件如下所示：

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>();
            });
}

我的ApplicationDbContext 有如下构造函数：

protected ApplicationDbContext() {}

public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options, IHttpContextAccessor contextAccessor) : base(options)
{
    _contextAccessor = contextAccessor;
}

我的Startup.cs 文件如下所示：

public Startup(IWebHostEnvironment env)
{
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)standard environment name (e.g: Local).
            .AddUserSecrets<Startup>()
            .AddEnvironmentVariables();

        Configuration = builder.Build();
        Environment = env;
}

public void ConfigureServices(IServiceCollection services)
{
        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

        services.AddIdentity<User, Role>(
            config => {...})
              .AddEntityFrameworkStores<ApplicationDbContext>()
              .AddDefaultTokenProviders()
              .AddUserValidator<IdendityUserValidator<User>>();
}

【问题讨论】：

在ConfigureServices 期间有Rollbar.RollbarException，您需要调查。对于该（或任何其他）异常，EF Core 无法使用应用程序服务来获取 DbContext 实例，并尝试使用不适用于您的情况的其他方式（设计时工厂、无参数构造函数），因此是第二个异常。
@IvanStoev，非常感谢您的指导。我在想 Rollbar 由于数据库上下文的问题而失败。我现在可以解决这个问题，它只是一个空的访问令牌，Rollbar 拒绝接受
@Elnoor 很高兴听到您解决了问题！可以写个简单的答案和accept it，让有类似问题的人受益，

标签： asp.net-core azure-devops entity-framework-core entity-framework-migrations

【解决方案1】：

Rollbar 配置失败，因为对于访问令牌，它需要一个非 null/空的字符串。由于我将 Rollbar 访问令牌存储在 Azure AppService 配置中并且 appsettings.json 没有列出访问令牌，因此发生了错误。因此，我使用虚拟非空字符串值将访问令牌添加到 appsettings.json。这有助于 Rollbar 自行配置而不会失败。

【讨论】：