Instance per matching lifetime scope, with default?

Question

I'd like to have an instance per matching lifetime scoped registration in Autofac, but occasionally need to request an instance from a global container (where there is no matching lifetime scope). In scenarios where no matching lifetime scope exists, I want to give a top-level instance instead of throwing an exception.

Is this possible?

Answer 1

I think you'd better extend Autofac by introducing a new lifetime option. I took the Autofac sources and modified them a bit:

public static class RegistrationBuilderExtensions
{
    public static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> InstancePerMatchingOrRootLifetimeScope<TLimit, TActivatorData, TRegistrationStyle>(this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> builder, params object[] lifetimeScopeTag)
    {
        if (lifetimeScopeTag == null) throw new ArgumentNullException("lifetimeScopeTag");
        builder.RegistrationData.Sharing = InstanceSharing.Shared;
        builder.RegistrationData.Lifetime = new MatchingScopeOrRootLifetime(lifetimeScopeTag);
        return builder;
    }
}

public class MatchingScopeOrRootLifetime: IComponentLifetime
{
    readonly object[] _tagsToMatch;

    public MatchingScopeOrRootLifetime(params object[] lifetimeScopeTagsToMatch)
    {
        if (lifetimeScopeTagsToMatch == null) throw new ArgumentNullException("lifetimeScopeTagsToMatch");

        _tagsToMatch = lifetimeScopeTagsToMatch;
    }

    public ISharingLifetimeScope FindScope(ISharingLifetimeScope mostNestedVisibleScope)
    {
        if (mostNestedVisibleScope == null) throw new ArgumentNullException("mostNestedVisibleScope");

        var next = mostNestedVisibleScope;
        while (next != null)
        {
            if (_tagsToMatch.Contains(next.Tag))
                return next;

            next = next.ParentLifetimeScope;
        }

        return mostNestedVisibleScope.RootLifetimeScope;
    }
}

Just add these classes to your project and register you component as:

builder.RegisterType<A>.InstancePerMatchingOrRootLifetimeScope("TAG");

I haven't tried it myself, but it should work.

Answer 2

Possible solution is to override registration in child lifetime scope.

Sample:

public enum Scopes
{
    TestScope
}

public class Test
{
   public string Description { get; set; }
}

public class Tester
{
    public void DoTest()
    {
        ContainerBuilder builder = new ContainerBuilder();
        builder.RegisterType<Test>()
            .OnActivating(args => args.Instance.Description = "FromRoot")
            .SingleInstance();
        var container = builder.Build();

        var scope = container.BeginLifetimeScope(Scopes.TestScope, b => b
            .RegisterType<Test>()
            .InstancePerMatchingLifetimeScope(Scopes.TestScope)
            .OnActivating(args => args.Instance.Description = "FromScope"));

        var test1 = container.Resolve<Test>();
        Console.WriteLine(test1.Description); //writes FromRoot

        var test2 = scope.Resolve<Test>();
        Console.WriteLine(test2.Description); //writes FromScope

        Console.ReadLine();
    }
}