当我尝试运行我的应用程序时出现错误
InvalidOperationException: Cannot resolve 'API.Domain.Data.Repositories.IEmailRepository' from root provider because it requires scoped service 'API.Domain.Data.EmailRouterContext'.
奇怪的是,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,但没有为它们引发错误。仅当我尝试使用 app.UseEmailingExceptionHandling(); 时才会发生错误线。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 = "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:我发现这个链接 https://github.com/aspnet/DependencyInjection/issues/578 导致我从这里更改了我的 Program.cs 文件的 BuildWebHost 方法
public static IWebHost BuildWebHost(string[] args)
{
return WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.Build();
}
对此
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,但它现在似乎有效。
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。您应该将依赖项移至 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);
}
}
获取作用域依赖实例的另一种方法是将服务提供者 (IServiceProvider
) 注入中间件构造函数,在 Invoke
方法中创建 scope
,然后从作用域中获取所需的服务:
using (var scope = _serviceProvider.CreateScope()) {
var _emailRepository = scope.ServiceProvider.GetRequiredService<IEmailRepository>();
//do your stuff....
}
查看 asp.net core dependency injection best practices tips tricks 中的在方法主体中解析服务,了解更多详细信息。
scope.ServiceProvider
而不是 _serviceProvider
。谢谢你。
ServiceProvider.CreateScope()
,请不要忘记 using Microsoft.Extensions.DependencyInjection;
。见这里:docs.microsoft.com/en-us/dotnet/api/…
中间件始终是单例的,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。
中间件支持 Invoke 方法上的方法注入,因此您只需将 IEmailRepository emailRepository 作为参数添加到该方法中,它将被注入那里并且在作用域中会很好。
public async Task Invoke(HttpContext context, IEmailRepository emailRepository)
{
....
}
您的 middleware
和 service
必须相互兼容才能通过 middleware
的 constructor
注入 service
。在这里,您的 middleware
已创建为 convention-based middleware
,这意味着它充当 singleton service
,并且您已将服务创建为 scoped-service
。因此,您不能将 scoped-service
注入 singleton-service
的构造函数,因为它会强制 scoped-service
充当 singleton
。但是,这是您的选择。
将您的服务作为参数注入 InvokeAsync 方法。如果可能的话,让你的服务成为一个单一的服务。将您的中间件转换为基于工厂的中间件。
Factory-based middleware
可以充当 scoped-service
。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 factory-based
中间件。
这仅用于演示。所以,我已经删除了所有其他代码。
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
:
public class TestService
{
}
不定期副业成功案例分享
Invoke
方法的一种特殊行为。但是,您可以通过 autofac IoC 库和属性注入实现类似的功能。请参阅ASP.NET Core MVC Dependency Injection via property or setter method?。