当我尝试运行我的应用时，我收到了错误
InvalidOperationException: Cannot resolve 'API.Domain.Data.Repositories.IEmailRepository' from root provider because it requires scoped service 'API.Domain.Data.EmailRouterContext'.
奇怪的是，这个EmailRepository和界面设置完全相同，因为我可以告诉所有其他存储库，但没有为它们抛出错误。只有在我尝试使用app.UseEmailingExceptionHandling（）时才会出现错误;线。这是我的一些Startup.cs文件。
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EmailRepository
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 = "errors@ourdomain.com";
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我的Program.cs文件的BuildWebHost方法
public static IWebHost BuildWebHost(string[] args)
{
return WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.Build();
}
到这个
public static IWebHost BuildWebHost(string[] args)
{
return WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.UseDefaultServiceProvider(options =>
options.ValidateScopes = false)
.Build();
}
我不知道究竟发生了什么，但它现在似乎有效。
答案 0 :(得分：67)
您在IEmailRepository课程中将Startup注册为范围服务。
这意味着您无法在Middleware中将其作为构造函数参数注入，因为Singleton中的构造函数注入只能解析Middleware个服务。您应该将依赖项移动到Invoke方法，如下所示：
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);
}
}
答案 1 :(得分：17)
中间件总是单例，因此您不能在中间件的构造函数中将作用域依赖项作为构造函数依赖项。
Middleware支持对Invoke方法进行方法注入，因此您只需将IEmailRepository emailRepository作为参数添加到该方法中，它就会在那里注入，并且可以作为范围使用。
public async Task Invoke(HttpContext context, IEmailRepository emailRepository)
{
....
}
答案 2 :(得分：16)
获取范围依赖实例的另一种方法是将服务提供者（IServiceProvider）注入到中间件构造函数中，在scope方法中创建Invoke，然后从范围：
using (var scope = _serviceProvider.CreateScope()) {
var _emailRepository = scope.ServiceProvider.GetRequiredService<IEmailRepository>);
//do your stuff....
}
在asp.net core dependency injection best practices tips tricks的方法主体中解析服务以获得更多详细信息。
答案 3 :(得分：0)
您的middleware和service必须彼此兼容，才能通过service的{{1}}注入constructor。在这里，您的middleware已创建为middleware，这意味着它充当convention-based middleware，并且您已将服务创建为singleton service。因此，您不能将scoped-service注入scoped-service的构造函数中，因为它会迫使singleton-service充当scoped-service。但是，这是您的选择。
singleton方法中。InvokeAsync转换为middleware。 factory-based可以充当Factory-based middleware。因此，您可以通过该中间件的构造函数注入另一个scoped-service。下面，我向您展示了如何创建scoped-service中间件。
这仅用于演示。因此，我删除了所有其他代码。
factory-based public class Startup
{
public Startup()
{
}
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<TestMiddleware>();
services.AddScoped<TestService>();
}
public void Configure(IApplicationBuilder app)
{
app.UseMiddleware<TestMiddleware>();
}
}
：
TestMiddleware public class TestMiddleware : IMiddleware
{
public TestMiddleware(TestService testService)
{
}
public Task InvokeAsync(HttpContext context, RequestDelegate next)
{
return next.Invoke(context);
}
}
：
TestService