无法访问已处置的对象。对象名称：AspNet Core/EF Core 项目中的“IServiceProvider”错误

Question

我正在使用 Entity Framework Core 编写一个 ASP.NET Core 应用程序。我也在使用 MediatR。

当我触发数据库更新时，无论是保存还是删除，我都会收到此错误：

无法访问已处置的对象。对象名称：'IServiceProvider'

有时会在第一次尝试时发生，有时在后续尝试时发生。我似乎找不到模式。 我设法做的是在调用await _applicationDbContext.SaveChangesAsync(cancellationToken); 的处理程序中打断点，尽管错误实际上是在await _mediator.Send(someRequestModel); 上的控制器中抛出的。引发错误后，应用程序进入中断模式并崩溃。

我将使用虚拟名称，但我认为这是相关代码：

控制器：

public MyController(IMediator mediator)
{
    _mediator = mediator ?? throw new ArgumentNullException(nameof(mediator));
}

[HttpDelete("{id}")]
public async void Delete(string id)
{
    await _mediator.Send(new DeleteRequestModel(Guid.Parse(id))); // error thrown here
}

处理程序：

public class DeleteCommandHandler : IRequestHandler<DeleteRequestModel>
{
    private readonly ApplicationDbContext _applicationDbContext;

    public DeleteCommandHandler(ApplicationDbContext applicationDbContext)
    {
        _applicationDbContext = applicationDbContext;
    }

    public async Task<Unit> Handle(DeleteRequestModel request, CancellationToken cancellationToken)
    {
        var item = _applicationDbContext.MyData.First(x => x.Id == request.Id);
        _applicationDbContext.MyData.Remove(item);

        await _applicationDbContext.SaveChangesAsync(cancellationToken); // pretty sure this errors out

        return Unit.Value;
    }
}

Startup.cs：

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

    services.AddDatabaseDeveloperPageExceptionFilter();

    services.AddDefaultIdentity<ApplicationUser>(options => options.SignIn.RequireConfirmedAccount = true)
        .AddEntityFrameworkStores<ApplicationAspNetUsersDbContext>();

    services.AddIdentityServer()
        .AddApiAuthorization<ApplicationUser, ApplicationAspNetUsersDbContext>();

    services.AddAuthentication()
        .AddIdentityServerJwt();
    services.AddControllers();
    services.AddRazorPages();
    // In production, the Angular files will be served from this directory
    services.AddSpaStaticFiles(configuration => { configuration.RootPath = "ClientApp/dist"; });

    services.AddSwaggerDocument();

    services.AddMediatR(AppDomain.CurrentDomain.Load("MySolution.MyProject.EntityFramework"));
    services.AddValidatorsFromAssembly(AppDomain.CurrentDomain.Load("MySolution.MyProject"));
    services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidatorPipelineBehavior<,>));

    services.AddSingleton(x =>
        new BlobServiceClient(Configuration.GetConnectionString("AzureBlobStorageConnection")));
    services.AddApplicationInsightsTelemetry(Configuration["APPINSIGHTS_CONNECTIONSTRING"]);

    services.Configure<ConnectionStrings>(Configuration.GetSection("ConnectionStrings"));
    services.Configure<AzureBlobStorage>(Configuration.GetSection("AzureBlobStorage"));
    services.Configure<ApplicationInsights>(Configuration.GetSection("ApplicationInsights"));
}

最后，这是堆栈跟踪，这次是更新操作：

at Microsoft.Extensions.DependencyInjection.ServiceLookup.ThrowHelper.ThrowObjectDisposedException()
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)
at MediatR.Pipeline.RequestExceptionActionProcessorBehavior`2.GetActionsForException(Type exceptionType, TRequest request, MethodInfo& actionMethodInfo)
at MediatR.Pipeline.RequestExceptionActionProcessorBehavior`2.<Handle>d__2.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()   
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at MediatR.Pipeline.RequestPostProcessorBehavior`2.<Handle>d__2.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()   
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at MediatR.Pipeline.RequestPreProcessorBehavior`2.<Handle>d__2.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()   
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)   
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at MySolution.Web.Controllers.MyController.< Patch >d__7.MoveNext() in
..\Controllers\MyController.cs:line 85

非常感谢任何帮助。

Answer 1

您在控制器中使用了异步 void。 Async void 应该只在特定场景中使用，在这种情况下，您应该使用 Task 作为返回类型。