Question

我正在使用Autofac实现一个命令处理程序模式，并使用它的装饰工具来处理交叉问题，例如日志记录，身份验证等。

我还有依赖项，我只希望作用于请求/响应管道的生命周期。

我在下面有一个示例实现：

public class Program
{
    public static void Main()
    {
        var builder = new ContainerBuilder();
        builder.RegisterAssemblyModules(typeof(HandlerModule).Assembly);
        builder.RegisterType<LifetimeScopeTester>().AsSelf()
            .InstancePerMatchingLifetimeScope("pipline");

        var container = builder.Build();

        using(var scope = container.BeginLifetimeScope("pipline")) {
            var pingHandler = scope.Resolve<IHandle<PingRequest, PingResponse>>();
            pingHandler.Handle(new PingRequest());
        }
    }
}

public class HandlerModule : Autofac.Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterAssemblyTypes(ThisAssembly)
            .As(type => type.GetInterfaces()
            .Where(interfaceType => interfaceType.IsClosedTypeOf(typeof (IHandle<,>)))
            .Select(interfaceType => new KeyedService("IHandle", interfaceType)));

        builder.RegisterGenericDecorator(
            typeof(SecondDecoratorHandler<,>),
            typeof(IHandle<,>),
            "IHandle"
        )
        .Keyed("SecondDecoratorHandler", typeof(IHandle<,>));

        builder.RegisterGenericDecorator(
            typeof(FirstDecoratorHandler<,>),
            typeof(IHandle<,>),
            "SecondDecoratorHandler"
        );
    }
}

public class LifetimeScopeTester {}

public interface IHandle<in TRequest, out TResponse> 
    where TRequest : class, IRequest<TResponse>
{
   TResponse Handle(TRequest request);
}

public interface IRequest<TResponse> {

}

public class PingRequest : IRequest<PingResponse> {

}

public class PingResponse {

}

public class PingHandler : IHandle<PingRequest, PingResponse> {
    public PingResponse Handle(PingRequest request) {
        Console.WriteLine("PingHandler");
        return new PingResponse();
    }
}

public class FirstDecoratorHandler<TRequest, TResponse> : IHandle<TRequest, TResponse>
    where TRequest : class, IRequest<TResponse>
{
    private readonly IHandle<TRequest, TResponse> _decoratedHandler;
    private readonly LifetimeScopeTester _lifetimeScopeTester;

    public FirstDecoratorHandler(IHandle<TRequest, TResponse> decoratedHandler,
        LifetimeScopeTester lifetimeScopeTester)
    {
        _decoratedHandler = decoratedHandler;
        _lifetimeScopeTester = lifetimeScopeTester;
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("FirstDecoratorHandler - LifetimeScopeTester[{0}]",
            _lifetimeScopeTester.GetHashCode());
        return _decoratedHandler.Handle(request);
    }
}

public class SecondDecoratorHandler<TRequest, TResponse> : IHandle<TRequest, TResponse> 
    where TRequest : class, IRequest<TResponse>
{
    private readonly IHandle<TRequest, TResponse> _decoratedHandler;
    private readonly LifetimeScopeTester _lifetimeScopeTester;

    public SecondDecoratorHandler(IHandle<TRequest, TResponse> decoratedHandler, LifetimeScopeTester lifetimeScopeTester)
    {
        _decoratedHandler = decoratedHandler;
        _lifetimeScopeTester = lifetimeScopeTester;
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("SecondDecoratorHandler - LifetimeScopeTester[{0}]", _lifetimeScopeTester.GetHashCode());
        return _decoratedHandler.Handle(request);
    }
}

正如您所看到的，我将pipleine包装在名为pipeline的范围内，这意味着每当我解析LifetimeScopeTester范围为pipeline时，我都会获得相同的实例。

我认为我可以替换

using(var scope = container.BeginLifetimeScope("pipline")) {
    var pingHandler = scope.Resolve<IHandle<PingRequest, PingResponse>>();
    pingHandler.Handle(new PingRequest());
}

与

var pingHandler = scope.Resolve<IHandle<PingRequest, PingResponse>>();
pingHandler.Handle(new PingRequest());

通过创建另一个做同样事情的装饰器。

我的第一直觉是：

public class LifetimeScopeDecoratorHandler<TRequest, TResponse> : IHandle<TRequest, TResponse> 
    where TRequest : class, IRequest<TResponse>
{
    private readonly ILifetimeScope _scope;
    private readonly IHandle<TRequest, TResponse> _decoratedHandler;

    public LifetimeScopeDecoratorHandlerAttempt1(ILifetimeScope scope, 
        IHandle<TRequest, TResponse> decoratedHandler)
    {
        _scope = scope;
        _decoratedHandler = decoratedHandler;
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("LifetimeScopeDecoratorHandler");

        TResponse response;

        using (_scope.BeginLifetimeScope("pipeline"))
        {
            response = _decoratedHandler.Handle(request);
        }

        return response;
    }
}

但decoratedHandler在注入时已经解决了，因此不起作用。

所以我试过了：

public class LifetimeScopeHandler<TRequest, TResponse> : IHandle<TRequest, TResponse> 
    where TRequest : class, IRequest<TResponse>
{
    private readonly ILifetimeScope _scope;
    private readonly Func<IHandle<TRequest, TResponse>> _decoratedHandlerFactory;

    public LifetimeScopeHandler(ILifetimeScope scope, 
        Func<IHandle<TRequest, TResponse>> decoratedHandlerFactory)
    {
        _scope = scope;
        _decoratedHandlerFactory = decoratedHandlerFactory;
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("LifetimeScopeDecoratorHandler");

        TResponse response;

        using (_scope.BeginLifetimeScope("pipeline"))
        {
            var decoratedHandler = _decoratedHandlerFactory();
            response = decoratedHandler.Handle(request);
        }

        return response;
    }
}

然而，当调用_decoratedHandlerFactory()尝试再次使用LifetimeScopeHandler装饰器包装内部处理程序时，这无限重复。

我正在努力实现的目标。

我在https://dotnetfiddle.net/hwujNI创建了一个dotnetfiddle来证明这个问题。

Answer 1

当Handle类的LifetimeScopeHandler方法调用decoratedHandlerFactory委托时，它会要求 Autofac 解析IHandle<TRequest, TResponse>这是LifetimeScopeHandler 1}}。这就是为什么你有StackOverflowException的原因。我们可以简化您的代码示例：

public class Foo
{
    public Foo(Func<Foo> fooFactory)
    {
        this._fooFactory = fooFactory;
    }
    private readonly Func<Foo> _fooFactory;

    public void Do()
    {
        Foo f = this._fooFactory();
        f.Do();
    }
}

即使只有Foo的单个实例，您也会有StackOverflowException

要解决此问题，您必须指明 Autofac decoratedHandlerFactory LifetimeScopeHandler代表不应是LifetimeScopeHandler的代表。

您可以使用WithParameter指示最后一个装饰器使用特定参数：

builder.RegisterGenericDecorator(
    typeof(LifetimeScopeHandler<,>),
    typeof(IHandle<,>),
    "FirstDecoratorHandler"
)
.WithParameter((pi, c) => pi.Name == "decoratedHandlerFactory",
               (pi, c) => c.ResolveKeyed("FirstDecoratorHandler", pi.ParameterType))
.As(typeof(IHandle<,>));

使用此配置，输出将为

LifetimeScopeHandler
  FirstDecoratorHandler - LifetimeScopeTester [52243212]
  SecondDecoratorHandler - LifetimeScopeTester [52243212]
  PingHandler

顺便说一句，您希望LifetimeScopeHandler成为一种特殊的装饰器，它将在特殊范围内创建内部IHandler<,>。

您可以通过让LifetimeScopeHandler为您创建正确的范围并解析之前的Ihandler来执行此操作。

public class LifetimeScopeHandler<TRequest, TResponse> 
    : IHandle<TRequest, TResponse> where TRequest : class, IRequest<TResponse>
{
    private readonly ILifetimeScope _scope;

    public LifetimeScopeHandler(ILifetimeScope scope)
    {
        this._scope = scope;
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("LifetimeScopeDecoratorHandler");

        using (ILifetimeScope s = this._scope.BeginLifetimeScope("pipline"))
        {
            var decoratedHandler = 
                s.ResolveKeyed<IHandle<TRequest, TResponse>>("FirstDecoratorHandler");
            TResponse response = decoratedHandler.Handle(request);
            return response;
        }
    }
}

此实现将要求LifetimeScopeHandler知道链上的第一个装饰器，我们可以通过在其构造函数上发送名称来绕过它。

public class LifetimeScopeHandler<TRequest, TResponse> 
    : IHandle<TRequest, TResponse> where TRequest : class, IRequest<TResponse>
{
    private readonly ILifetimeScope _scope;
    private readonly String _previousHandlerName; 

    public LifetimeScopeHandler(ILifetimeScope scope, String previousHandlerName)
    {
        this._scope = scope;
        this._previousHandlerName = previousHandlerName; 
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("LifetimeScopeDecoratorHandler");

        using (ILifetimeScope s = this._scope.BeginLifetimeScope("pipline"))
        {
            var decoratedHandler = 
                s.ResolveKeyed<IHandle<TRequest, TResponse>>(previousHandlerName);
            TResponse response = decoratedHandler.Handle(request);
            return response;
        }
    }
}

你必须像这样注册：

builder.RegisterGenericDecorator(
         typeof(LifetimeScopeHandler<,>),
         typeof(IHandle<,>),
         "FirstDecoratorHandler"
       )
       .WithParameter("previousHandlerName", "FirstDecoratorHandler")
       .As(typeof(IHandle<,>));

我们也可以通过不使用RegisterGenericDecorator方法绕过一切。

如果我们这样注册LifetimeScopeHandler：

builder.RegisterGeneric(typeof(LifetimeScopeHandler<,>))
       .WithParameter((pi, c) => pi.Name == "decoratedHandler",
                      (pi, c) =>
                      {
                          ILifetimeScope scope = c.Resolve<ILifetimeScope>();
                          ILifetimeScope piplineScope = scope.BeginLifetimeScope("pipline");
                          var o = piplineScope.ResolveKeyed("FirstDecoratorHandler", pi.ParameterType);
                          scope.Disposer.AddInstanceForDisposal(piplineScope);
                          return o;
                      })
       .As(typeof(IHandle<,>));

LifetimeScopeHandler现在看起来像所有装饰者：

public class LifetimeScopeHandler<TRequest, TResponse> 
  : IHandle<TRequest, TResponse> where TRequest : class, IRequest<TResponse>
{
    private readonly IHandle<TRequest, TResponse> _decoratedHandler;

    public LifetimeScopeHandler(IHandle<TRequest, TResponse> decoratedHandler)
    {
        this._decoratedHandler = decoratedHandler;
    }

    public TResponse Handle(TRequest request)
    {
        Console.WriteLine("LifetimeScopeDecoratorHandler");

        TResponse response = this._decoratedHandler.Handle(request);
        return response;
    }
}

顺便说一下，如果您在范围中使用多个IHandler<,>并且需要一个pipline范围，则此解决方案可能会出现问题。要解决这个问题，你可以看到这个dotnetfiddle：https://dotnetfiddle.net/rQgy2X，但在我看来这很复杂，你可能不需要它。

Autofac终身范围装饰器

1 个答案: