c# - 注册装饰器与注册 IEnumerable 冲突

Question

我正在使用 simpleinjector 2.3.0.0 和 .net 4.5。

我一直在尝试注册一个依赖于 IEnumerable 的工厂、一个事物的实例以及一个工作单元装饰器。 (除其他事项外)

这是我的工厂:

public class ThingFactory : IThingFactory
{
    private readonly IEnumerable<IThing> things;

    public ThingFactory (IEnumerable<IThing> things)
    {
        this.things= things;
    }

    public IThing GetThing(ThingType thingType)
    {
     return things.FirstOrDefault(t => t.IsApplicable(thingType));
    }
}

这是我对 IThing 的实现

 public class ThingOne: IThing
{
     private IThingFactory thingFactory;

    public ThingOne(IThingFactory thingFactory)
    {
        this.thingFactory= thingFactory;
    }

    public void Execute(MyDto myDto)
    {
       //do stuff
      //get the next approiate IThing out of the factory and execute
    }

    public bool IsApplicable(ThingType thingType)
    {
        return thingType == ThingType.ThingOne;
    }

我的注册是

  container.RegisterAll<IThing>(
            from tp in typeof (IThing).Assembly.GetExportedTypes()
            where !tp.IsAbstract
            where typeof (IThing).IsAssignableFrom(tp)
            select tp);

   container.Register<IThingFactory , ThingFactory>();

这绝对没问题，我可以无一异常(exception)地验证容器。但是，当我还将以下注册添加到容器时，出现异常

 container.RegisterDecorator(typeof(ICommandHandler<,>),    
 typeof(UnitOfWorkDecorator<,>));

装饰器是一个 Nhibernate UnitOFWork，它管理一个 Nhibernate 事务(这并不重要)(遵循此模式 https://cuttingedge.it/blogs/steven/pivot/entry.php?id=91)

  public class UnitOfWorkDecorator<TCommand, TResult>
    : ICommandHandler<TCommand, TResult> 
    where TCommand : ICommand
{

    public UnitOfWorkDecorator(
        ICommandHandler<TCommand, TResult> decoratedCommandHandler)
    {
        this.currentSessionContextService = currentSessionContextService;
        this.decoratedCommandHandler = decoratedCommandHandler;
    }

    public void Handle(TCommand command)
    {
          //start my nhibernate transaction
          decoratedCommandHandler.Handle(command);

          //commit the transaction                       
    }

所以无论如何，当我添加装饰器时，我得到以下异常。当我打电话时

  container.Verify();

然而，当我删除装饰器注册时，一切又好了。

Topshelf v3.1.107.0, .NET Framework v4.0.30319.18052
Topshelf.Hosts.ConsoleRunHost Error: 0 : An exception occurred, System.Reflectio
n.TargetInvocationException: Exception has been thrown by the target of an invoc
ation. ---> System.InvalidOperationException: The configuration is invalid. Crea
ting the instance for type IThingManager failed. The registered delegate for t
ype IThingManager threw an exception. The registered delegate for type IThingFa
ctory threw an exception. The registered delegate for type IEnumerable<IThing> th
rew an exception. No registration for type ThingOne could be found a
nd an implicit registration could not be made.  ---> SimpleInjector.ActivationEx
ception: The registered delegate for type IThingManager threw an exception. Th
e registered delegate for type IThingFactory threw an exception. The registered d
elegate for type IEnumerable<IThing> threw an exception. No registration for type
ThingOne could be found and an implicit registration could not be m
ade.  ---> SimpleInjector.ActivationException: The registered delegate for type
IThingFactory threw an exception. The registered delegate for type IEnumerable<IThing>     
threw an exception. No registration for type ThingOne could be
found and an implicit registration could not be made.  ---> SimpleInjector.Activ
ationException: The registered delegate for type IEnumerable<IThing> threw an exc
eption. No registration for type ThingOne could be found and an impl
icit registration could not be made.  ---> SimpleInjector.ActivationException: N
o registration for type ThingOne could be found and an implicit regi
stration could not be made.

堆栈跟踪:

at SimpleInjector.Container.ThrowNotConstructableException(Type concreteType)
at SimpleInjector.Container.ThrowMissingInstanceProducerException(Type servic
eType)at SimpleInjector.Container.GetRegistration(Type serviceType, Boolean throwOn
 Failure)   at SimpleInjector.Advanced.ContainerControlledCollection`1.   
 <>c__DisplayClass1
0.<ToLazyInstanceProducer>b__f()   at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()     at     
SimpleInjector.Advanced.ContainerControlledCollection`1.<SimpleInjector.Ad
vanced.IContainerControlledCollection.GetRelationships>b__1(Lazy`1 p)
at System.Linq.Enumerable.WhereSelectListIterator`2.MoveNext()
at System.Linq.Enumerable.<SelectManyIterator>d__31`3.MoveNext()
at System.Linq.Enumerable.<DistinctIterator>d__81`1.MoveNext()
at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
at SimpleInjector.Advanced.ContainerControlledCollection`1.SimpleInjector.Adv
anced.IContainerControlledCollection.GetRelationships()
at SimpleInjector.Extensions.Decorators.DecoratorHelpers.ContainerControlledC
ollectionRegistration.GetRelationshipsCore()
at SimpleInjector.Registration.GetRelationships()
at SimpleInjector.InstanceProducer.GetRelationships()
at SimpleInjector.Container.OnExpressionBuilt(ExpressionBuiltEventArgs e, Ins
tanceProducer instanceProducer)
at SimpleInjector.InstanceProducer.BuildExpressionInternal()
at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()
at SimpleInjector.InstanceProducer.BuildExpression()
--- End of inner exception stack trace ---
at SimpleInjector.InstanceProducer.BuildExpression()
at SimpleInjector.Advanced.DefaultConstructorInjectionBehavior.BuildParameter
Expression(ParameterInfo parameter)
at SimpleInjector.Registration.BuildParameterExpressionFor(ParameterInfo para
meter)
at SimpleInjector.Registration.<BuildNewExpression>b__1a(<>f__AnonymousTypef`
2 <>h__TransparentIdentifier18)
at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
at SimpleInjector.Registration.BuildNewExpression(Type serviceType, Type impl
ementationType)
at SimpleInjector.Registration.BuildTransientExpression[TService,TImplementat
ion]()
at SimpleInjector.Lifestyles.TransientLifestyle.TransientLifestyleRegistratio
n`2.BuildExpression()
at SimpleInjector.InstanceProducer.BuildExpressionInternal()
at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()
at SimpleInjector.InstanceProducer.BuildExpression()
--- End of inner exception stack trace ---
at SimpleInjector.InstanceProducer.BuildExpression()
at SimpleInjector.Advanced.DefaultConstructorInjectionBehavior.BuildParameter
Expression(ParameterInfo parameter)
at SimpleInjector.Registration.BuildParameterExpressionFor(ParameterInfo para
meter)
at SimpleInjector.Registration.<BuildNewExpression>b__1a(<>f__AnonymousTypef`
2 <>h__TransparentIdentifier18)
at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
at SimpleInjector.Registration.BuildNewExpression(Type serviceType, Type impl
ementationType)
at SimpleInjector.Registration.BuildTransientExpression[TService,TImplementat
ion]()
at SimpleInjector.Lifestyles.TransientLifestyle.TransientLifestyleRegistratio
n`2.BuildExpression()
at SimpleInjector.InstanceProducer.BuildExpressionInternal()
at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()
at SimpleInjector.InstanceProducer.BuildInstanceCreator(Object& createdInstan
ce)
at SimpleInjector.InstanceProducer.GetInstance()
--- End of inner exception stack trace ---
at SimpleInjector.InstanceProducer.GetInstance()
at SimpleInjector.InstanceProducer.Verify()
--- End of inner exception stack trace ---
at SimpleInjector.InstanceProducer.Verify()
at SimpleInjector.Container.VerifyProducers(InstanceProducer[] producersToVer
ify)
at SimpleInjector.Container.ValidateRegistrations()
at SimpleInjector.Container.Verify()

谢谢你的帮助

编辑 - ThingManager 是入口点，如下所示:

   public class ThingManager : IThingManager
{
    private readonly IThingFactory thingFactory;

    public ThingManager(IThingFactory thingFactory)
    {
        this.thingFactory = thingFactory;
    }

    public void Run(MyDto myDto)
    {
        var firstThing = thingFactory.GetThing(ThingType.ThingOne);
        firstThing.Execute(myDto);
    }
}

Answer 1

问题是由您的代码中的循环引用引起的:ThingFactory取决于 IEnumerable<IThing> , 这取决于 ThingOne , 这取决于 ThingFactory ，这将关闭循环。

不幸的是由于 a bug在 Simple Injector 2.3 中，描述循环引用的真正错误被隐藏，并抛出一条表达能力较差(在本例中甚至不正确)的消息。此错误已在 Simple Injector 2.3.5 中得到修复.

尽管循环引用存在于您的代码库中，Verify方法仅在注册装饰器时注意到此错误。内部ContainerControlledCollection<T>导致注册的元素被预编译，这允许 InstanceProducer注意循环的实例。没有 ContainerControlledCollection<T>即使在解析类型时，集合的评估也更加延迟，这完全隐藏了这个错误。然而，您设计中的这个怪癖可能仍然会在以后引起各种问题。

对于即将推出的 Simple Injector 2.4 ContainerControlledCollection<T>在 Verify() 的情况下实际上会更懒惰地提高性能不被调用(这对于具有深层对象图和包含许多项的集合的应用程序有意义)，但这意味着即使使用装饰器，验证器也不会抛出异常。

Simple Injector 2.4 不抛出异常的行为其实是正确的(事实上 2.3 和 2.3.5 抛出异常可以被认为是一个错误)，因为 Simple Injector 的目标是在构建对象时防止 stackoverflow 异常图(当调用 GetInstance 时)。由于 IEnumerable<T> 之后类型的创建被延迟使用(解析 IEnumerable<T> 不解析实例；只有迭代集合才解析)，没有 stackoverflow 异常。

虽然在您的代码中使用循环引用可能会产生代码异味，但在您的代码中它可能只会导致代码中的递归(但不会导致 stackoverflow)，这可能是预期的行为。

您仍然可能想要重新考虑设计，因为递归深度为 10(假设您有 10 个东西并调用工厂以获取列表中的下一个东西)，这将触发创建 55 个东西(10 倍于第一个元素，9 个第二个元素，8 个第三个，... 1 个第十个元素)，这可能不是您所期望的。