无法从根提供程序 .Net Core 2 解析范围服务 [英] Cannot resolve scoped service from root provider .Net Core 2

问题描述

当我尝试运行我的应用程序时出现错误

When I try to run my app I get the error

InvalidOperationException: Cannot resolve 'API.Domain.Data.Repositories.IEmailRepository' from root provider because it requires scoped service 'API.Domain.Data.EmailRouterContext'.

奇怪的是，据我所知，这个 EmailRepository 和界面的设置与我的所有其他存储库完全相同，但没有为它们抛出任何错误.该错误仅在我尝试使用 app.UseEmailingExceptionHandling(); 时发生；线.这是我的一些 Startup.cs 文件.

What's odd is that this EmailRepository and interface is set up exactly the same as far as I can tell as all of my other repositories yet no error is thrown for them. The error only occurs if I try to use the app.UseEmailingExceptionHandling(); line. Here's some of my Startup.cs file.

public class Startup
{
    public IConfiguration Configuration { get; protected set; }
    private APIEnvironment _environment { get; set; }

    public Startup(IConfiguration configuration, IHostingEnvironment env)
    {
        Configuration = configuration;

        _environment = APIEnvironment.Development;
        if (env.IsProduction()) _environment = APIEnvironment.Production;
        if (env.IsStaging()) _environment = APIEnvironment.Staging;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        var dataConnect = new DataConnect(_environment);

        services.AddDbContext<GeneralInfoContext>(opt => opt.UseSqlServer(dataConnect.GetConnectString(Database.GeneralInfo)));
        services.AddDbContext<EmailRouterContext>(opt => opt.UseSqlServer(dataConnect.GetConnectString(Database.EmailRouter)));

        services.AddWebEncoders();
        services.AddMvc();

        services.AddScoped<IGenInfoNoteRepository, GenInfoNoteRepository>();
        services.AddScoped<IEventLogRepository, EventLogRepository>();
        services.AddScoped<IStateRepository, StateRepository>();
        services.AddScoped<IEmailRepository, EmailRepository>();
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole();

        app.UseAuthentication();

        app.UseStatusCodePages();
        app.UseEmailingExceptionHandling();

        app.UseMvcWithDefaultRoute();
    }
}

这是电子邮件存储库

public interface IEmailRepository
{
    void SendEmail(Email email);
}

public class EmailRepository : IEmailRepository, IDisposable
{
    private bool disposed;
    private readonly EmailRouterContext edc;

    public EmailRepository(EmailRouterContext emailRouterContext)
    {
        edc = emailRouterContext;
    }

    public void SendEmail(Email email)
    {
        edc.EmailMessages.Add(new EmailMessages
        {
            DateAdded = DateTime.Now,
            FromAddress = email.FromAddress,
            MailFormat = email.Format,
            MessageBody = email.Body,
            SubjectLine = email.Subject,
            ToAddress = email.ToAddress
        });
        edc.SaveChanges();
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    private void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
                edc.Dispose();
            disposed = true;
        }
    }
}

最后是异常处理中间件

public class ExceptionHandlingMiddleware
{
    private const string ErrorEmailAddress = "[e-mail]";
    private readonly IEmailRepository _emailRepository;

    private readonly RequestDelegate _next;

    public ExceptionHandlingMiddleware(RequestDelegate next, IEmailRepository emailRepository)
    {
        _next = next;
        _emailRepository = emailRepository;
    }

    public async Task Invoke(HttpContext context)
    {
        try
        {
            await _next.Invoke(context);
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(context, ex, _emailRepository);
        }
    }

    private static Task HandleExceptionAsync(HttpContext context, Exception exception,
        IEmailRepository emailRepository)
    {
        var code = HttpStatusCode.InternalServerError; // 500 if unexpected

        var email = new Email
        {
            Body = exception.Message,
            FromAddress = ErrorEmailAddress,
            Subject = "API Error",
            ToAddress = ErrorEmailAddress
        };

        emailRepository.SendEmail(email);

        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int) code;
        return context.Response.WriteAsync("An error occured.");
    }
}

public static class AppErrorHandlingExtensions
{
    public static IApplicationBuilder UseEmailingExceptionHandling(this IApplicationBuilder app)
    {
        if (app == null)
            throw new ArgumentNullException(nameof(app));
        return app.UseMiddleware<ExceptionHandlingMiddleware>();
    }
}

更新:我找到了这个链接 https://github.com/aspnet/DependencyInjection/issues/578这导致我从此更改了 Program.cs 文件的 BuildWebHost 方法

Update: I found this link https://github.com/aspnet/DependencyInjection/issues/578 which led me to change my Program.cs file's BuildWebHost method from this

public static IWebHost BuildWebHost(string[] args)
{
    return WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .Build();
}

到这里

public static IWebHost BuildWebHost(string[] args)
{
    return WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .UseDefaultServiceProvider(options =>
            options.ValidateScopes = false)
        .Build();
}

我不知道到底发生了什么，但现在似乎可以工作了.

I don't know what exactly is going on but it seems to work now.

推荐答案

您在 Startup 类中将 IEmailRepository 注册为范围服务.这意味着您不能将其作为构造函数参数注入Middleware，因为只有Singleton 服务可以通过Middleware 中的构造函数注入来解析.您应该像这样将依赖项移动到 Invoke 方法:

You registered the IEmailRepository as a scoped service, in the Startup class. This means that you can not inject it as a constructor parameter in Middleware because only Singleton services can be resolved by constructor injection in Middleware. You should move the dependency to the Invoke method like this:

public ExceptionHandlingMiddleware(RequestDelegate next)
{
    _next = next;
}

public async Task Invoke(HttpContext context, IEmailRepository emailRepository)
{
    try
    {
        await _next.Invoke(context);
    }
    catch (Exception ex)
    {
        await HandleExceptionAsync(context, ex, emailRepository);
    }
}

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