Autofac behaves differently than the Microsoft ServiceProvider with lambda registrations that return null #60
Comments
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Hey @scottt732, thanks for reporting this. I am not sure which constellation led to your error but what you are trying to do actually works the same as the service-provider created by Microsoft and is therefor indeed a full-replacement for it. Here the code I've used public class DepTests
{
private class SomeDependency {}
[Fact]
public void DependencyRegisteredResolved()
{
var serviceCollection = new ServiceCollection();
serviceCollection.AddTransient<SomeDependency>();
var containerBuilder = new ContainerBuilder();
containerBuilder.Populate(serviceCollection);
var container = containerBuilder.Build();
var autofacServiceProvider = new AutofacServiceProvider(container);
var service = autofacServiceProvider.GetService<SomeDependency>();
Assert.NotNull(service);
}
[Fact]
public void DependencyOptionalResolved()
{
var serviceCollection = new ServiceCollection();
var containerBuilder = new ContainerBuilder();
containerBuilder.Populate(serviceCollection);
var container = containerBuilder.Build();
var autofacServiceProvider = new AutofacServiceProvider(container);
var service = autofacServiceProvider.GetService<SomeDependency>();
Assert.Null(service);
}
}I've created a repository that you can clone and try to find out what went wrong for you. |
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@alsami Note the first test in the @scottt732 example doesn't use Autofac: serviceCollection.AddTransient<ConcreteSampleService1>(sp => null);
var serviceProvider = serviceCollection.BuildServiceProvider();
var service = serviceProvider.GetService<ConcreteSampleService1>();The issue here is that the Microsoft service provider apparently allows you to register a dependency that returns null while Autofac does not. I'm not sure this is something we actually want to fix, though, so I think there's still no action required.
Long story already too long, I think this is a "won't fix." If Microsoft adds this to their tests and requires all of the conforming container implementations to support it, we can revisit it at that time. |
Yeah missed that one thanks for the hint :) |
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Thanks for the quick responses.
I just wanted to clarify a few points a bit above for future Googlers' sake. "the Microsoft service provider apparently allows you to register a dependency that returns null while Autofac does not." [Fact]
public void BuildAutofacServiceProvider_WhenLambdaServiceRegistrationViaAutofac1_UnfortunatelyThrowsException()
{
var containerBuilder = new ContainerBuilder();
containerBuilder.Register<ConcreteSampleService1>(cc => null);
var container = containerBuilder.Build();
var serviceProvider = new AutofacServiceProvider(container);
var service = serviceProvider.GetService<ConcreteSampleService1>();
// Fail --> throws DependencyResolutionException (see below)
Assert.Null(service);
}"The difference between [Fact]
public void BuildAutofacServiceProvider_WhenLambdaServiceRegistrationViaMs_ReturnsNullServiceReference()
{
var serviceCollection = new ServiceCollection();
serviceCollection.AddTransient<ConcreteSampleService1>(sp => null);
var serviceProvider = serviceCollection.BuildServiceProvider();
var service = serviceProvider.GetService<ConcreteSampleService1>();
Assert.Null(service);
Assert.Throws<InvalidOperationException>(() => serviceProvider.GetRequiredService<ConcreteSampleService1>());
}
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Describe the bug
I'm not sure this is a bug or maybe something worth calling out in the documentation. I just wanted to bring it to your attention in case you're trying to be a 100% drop-in replacement for Microsoft's
IServiceProviderimplementation.I ran into a runtime exception resolving a service graph after introducing Autofac to an existing .NET Core app. It was a straightforward fix & a code smell in our codebase, but it was surprising nonetheless.
To reproduce
Reproduction of the issue, ideally in a unit test format.
Full exception with stack trace:
Assembly/dependency versions:
I was also able to reproduce this in Autofac 4.9.4 + Autofac.Extensions.DependencyInjection 4.4.0
Additional context
Add any other context about the problem here.
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