c# - Autofac.Core.Registration.ComponentNotRegisteredException

Question

我试图在我的应用程序中实现 CQRS 模式。所以我在这里找到了如何从程序集中注册所有命令处理程序:Autofac resolve dependency in CQRS CommandDispatcher

但这对我来说效果不佳。这是代码:

        containerBuilder.RegisterAssemblyTypes(assembly)
            .AsClosedTypesOf(typeof(ICommandHandler<>));

        containerBuilder.RegisterAssemblyTypes(assembly)
            .AsClosedTypesOf(typeof(IQueryHandler<,>));

搬运工工厂

 public class CqrsHandlerFactory : ICqrsHandlerFactory
{
    private readonly IContainer container;

    public CqrsHandlerFactory(IContainer container)
    {
        this.container = container;
    }

    public ICommandHandler<TCommand> GetCommandHandler<TCommand>(TCommand command) where TCommand : class, ICommand
    {
        return container.Resolve<ICommandHandler<TCommand>>();
    }

    public IQueryHandler<TQuery, object> GetQueryHandler<TQuery>(TQuery query) where TQuery : class, IQuery
    {
        return container.Resolve<IQueryHandler<TQuery, object>>();
    }
}

公共(public)汽车

 public class CqrsBus : ICqrsBus
{
    private readonly ICqrsHandlerFactory cqrsHandlerFactory;

    public CqrsBus(ICqrsHandlerFactory cqrsHandlerFactory)
    {
        this.cqrsHandlerFactory = cqrsHandlerFactory;
    }

    public void ExecuteCommand(ICommand command)
    {
        var handler = cqrsHandlerFactory.GetCommandHandler(command);
        if (handler == null)
            throw new NotImplementedHandlerException(string.Format("Cannot find handler for {0}", command.GetType()));
        handler.Handle(command);
    }

    public TResult RunQuery<TResult>(IQuery query)
    {
        var handler = cqrsHandlerFactory.GetQueryHandler(query);
        if (handler == null)
            throw new NotImplementedHandlerException(string.Format("Cannot find handler for {0}", query.GetType()));
        return (TResult)handler.Handle(query);
    }
}

异常(exception)

An exception of type 'Autofac.Core.Registration.ComponentNotRegisteredException' occurred in Autofac.dll but was not handled in user code Additional information: The requested service 'PromocjeWsieciowkach.Messaging.Core.ICommandHandler`1[[PromocjeWsieciowkach.Messaging.Core.ICommand, PromocjeWsieciowkach.Messaging.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' has not been registered. To avoid this exception, either register a component to provide the service, check for service registration using IsRegistered(), or use the ResolveOptional() method to resolve an optional dependency.

堆栈跟踪

at Autofac.ResolutionExtensions.ResolveService(IComponentContext context, Service service, IEnumerable1 parameters)
at Autofac.ResolutionExtensions.Resolve[TService](IComponentContext context, IEnumerable1 parameters) at PromocjeWsieciowkach.Messaging.Factories.CqrsHandlerFactory.GetCommandHandler[TCommand](TCommand command) in C:\Users\Daniel\Desktop\PromocjeWsieciowkach\src\PromocjeWsieciowkach.Messaging\Factories\CqrsHandlersFactory.cs:line 17 at PromocjeWsieciowkach.Messaging.Bus.CqrsBus.ExecuteCommand(ICommand command) in C:\Users\Daniel\Desktop\PromocjeWsieciowkach\src\PromocjeWsieciowkach.Messaging\Bus\CqrsBus.cs:line 17 at PromocjeWsieciowkach.Controllers.PostController.Index() in C:\Users\Daniel\Desktop\PromocjeWsieciowkach\src\PromocjeWsieciowkach\Controllers\PostController.cs:line 20 at lambda_method(Closure , Object , Object[] ) at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.d__28.MoveNext()

那么我做错了什么？

Answer 1

您的代码和异常消息清楚地显示了问题。总之，您的异常消息解释说:

The requested service 'ICommandHandler<ICommand>' has not been registered.

换句话说，您请求的是 ICommandHandler<ICommand>而不是 ICommandHandler<TestCommand> .这可以在这里看到:

public void ExecuteCommand(ICommand command)
{
    var handler = cqrsHandlerFactory.GetCommandHandler(command);
    // ...
}

C# 编译器将类型推断应用于 GetCommandHandler<T>称呼。所以下面的代码是实际的调用:

var handler = cqrsHandlerFactory.GetCommandHandler<ICommand>(command);

您应该更改 ICrqsBus.ExecuteCommand方法如下:

public void ExecuteCommand<TCommand>(TCommand command)
{
    // You can merge the factory and your CqrsBus. Splitting them is useless.
    var handler = cqrsHandlerFactory.GetCommandHandler<TCommand>();
    // You don't need then null check; Autofac never returns null.
    handler.Handle(command);
}

如果您无法制作 ExecuteCommand方法泛型(例如，因为您在编译时不知道命令类型)，您应该使用反射 API 构建泛型类型，如下所示:

public class CqrsBus : ICqrsBus
{
    private readonly IComponentContext context;

    public CqrsBus(IComponentContext context)
    {
        this.context = context;
    }

    public void ExecuteCommand(ICommand command)
    {
        Type handlerType = typeof(ICommandHandler<>).MakeGenericType(command.GetType());
        dynamic handler = this.context.Resolve(handlerType);
        void handler.Execute((dynamic)command);
    }
}