Simple Injector. How to reuse a decorator class more than once in object's decorator chain using Scoped lifestyle

Question

I want to reuse same class more than once in a chain of decorated objects like this.

InstrumentedTargetDecorator -> ResilientTargetDecorator -> InstrumetedTargetDecorator -> Target

Note that InstrumentedTargetDecorator is used twice here on purpose.

This is how SimpleInjector syntax looks to get the above wired up

container.Register<ITarget, Target>(Lifestyle.Scoped);
container.RegisterDecorator(
    typeof(ITarget), typeof(InstrumentationTargetDecorator), Lifestyle.Scoped);
container.RegisterDecorator(
    typeof(ITarget), typeof(ResilienceTargetDecorator), Lifestyle.Scoped);
container.RegisterDecorator(
    typeof(ITarget), typeof(InstrumentationTargetDecorator), Lifestyle.Scoped);

If run as is with standard options this will throw producing following warnings

-[Ambiguous Lifestyles] The registration for ITarget (Async Scoped) maps to the same implementation (InstrumentationTargetDecorator) as the registration for ITarget (Scoped) does, but the registration maps to a different lifestyle. This will cause each registration to resolve to a different instance.

-[Ambiguous Lifestyles] The registration for ITarget (Scoped) maps to the same implementation (InstrumentationTargetDecorator) as the registration for ITarget (Async Scoped) does, but the registration maps to a different lifestyle. This will cause each registration to resolve to a different instance.

(2 warning messages reported because there are 2 decorator registrations of InstrumentationTargetDecorator)

Only way I could actually get it to work is by not running .Verify() (and setting EnableAutoVerification to false). Needless to say this is not a viable option in practice.

There doesn't seem to be any way to suppress this warning for a single decorator registration, because the regular suppress warning playbook doesn't work for decorators i.e. decorator registrations aren't actually retrievable at registration time e.g.

Container.GetRegistration<ITarget>() produces the original/non-decorated instance (I suspect that's because decorators aren't really resolved until the object graph is built)

If I try to force the graph building

Container.Verify(VerificationOption.VerifyOnly);

var registration = Container.GetRegistration<ITarget>()?.Registration;
registration?.SuppressDiagnosticWarning(DiagnosticType.AmbiguousLifestyles, "I'm right");

Container.Verify();

I can get my hands on the outermost most InstrumentationTargetDecorator which then allows me to suppress one of the warning messages, but not the other one.

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Some more context and the actual program below

Originally I had this setup like this

ResilientTargetDecorator -> Target

(ResilientTargetDecorator wraps Target)

Then I decided to measure how long the Target method call takes, so I introduced a new decorator

ResilientTargetDecorator -> InstrumetedTargetDecorator -> Target

So far so good, this works as expected.

But what if I now want to re-use that instrumentation decorator to also measure how long the entire chain takes including the resilient target decorator ?

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Program to reproduce this issue here

https://dotnetfiddle.net/zESxqc

Answer 1

You encountered a bug in Simple Injector. I will try to fix this in the next patch release. This bug has been fixed in v5.3.3.

As workaround, when working in an older release, create a derivative of the decorator inside your Composition Root and make that derivative the second registration. Hopefully this suppresses the invalid warning:

class Derivative: InstrumentationTargetDecorator { ...}


container.Register<ITarget, Target>(Lifestyle.Scoped);
 container.RegisterDecorator(typeof(ITarget), typeof(InstrumentationTargetDecorator), Lifestyle.Scoped);
 container.RegisterDecorator(typeof(ITarget), typeof(ResilienceTargetDecorator), Lifestyle.Scoped);
 container.RegisterDecorator(typeof(ITarget), typeof(Derivative), Lifestyle.Scoped);