asp.net - Get same instance of a component registered with Autofac as InstancePerLifetimeScope in Global.asax methods as is injected into a controllers?

Question

I have a situation where I need to manually instantiate some objects in Application_BeginRequest that are dependent on some of the same components that I've registered with Autofac. I'd like to use the same instances of components that I've registered with Autofac with InstancePerLifetimeScope for injection into my MVC and WebAPI controllers. My config for both MVC and Web API works as expected, and an example of a component registration looks like so:

builder.Register(c => new MyDbContext()).AsSelf().InstancePerLifetimeScope();

Now I want to use that same instance in the class I'm instantiating in Application_BeginRequest. I've tried the following methods:

//Tried with MVC controllers
DependencyResolver.Current.GetService<MyDbContext>()));
AutofacDependencyResolver.Current.ApplicationContainer.Resolve<MyDbContext>()));
AutofacDependencyResolver.Current.RequestLifetimeScope.Resolve<MyDbContext>()));
//Tried with Web API controllers
GlobalConfiguration.Configuration.DependencyResolver.GetService(typeof(MyDbContext))

But none give me what I'm looking for, even at later points in the request lifecylce (ie, beyond BeginRequest). As an aside, I need this to work with the Web API configuration, but I tried the first 3 methods just to see if I could get any of the resolved instances to match up with what Autofac is injecting.

I have what I believe is a decent understanding of lifetime scopes in Autofac and my assumption is that the instances that are being resolved for my application's controllers are in a child scope that the none of the above 4 methods are pointed towards, but it's fuzzy to me what each of the above methods is trying to do in regard to which scope they are looking at and how they decide. What's even fuzzier is what lifetime scopes Autofac is automatically creating for the components that are ultimately injected into my controllers and when they're created.

Clarification on the points above would be a big bonus, but my primary question here is how do I get Autofac to hand me the same instances of registered components in Global.asax that it resolves for Web API and MVC controllers?

Answer 1

Well, I think you should try changing .InstancePerLifetimeScope() into .InstancePerRequest();

As Autofac says about InstancePerLifetimeScope:

When you resolve the instance per lifetime scope component, you get a single instance per nested scope (e.g., per unit of work).

So when you do Resolve<MyDbContext>() you are probably doing it in a different Lifetime scope than you controller (I guess it's because you're doing an explicit resolution); that's why you're getting a diffent instance.

InstancePerRequest instead:

Some application types naturally lend themselves to “request” type semantics, for example ASP.NET web forms and MVC applications. In these application types, it’s helpful to have the ability to have a sort of “singleton per request.”

The begin phase of your request is already in the request phase, so you shoud get the same instance there and inside your controllers.

Instance per request builds on top of instance per matching lifetime scope by providing a well-known lifetime scope tag, a registration convenience method, and integration for common application types.

Based on this, probably, you can also go for the .InstancePerMatchingLifetimeScope("myrequest"), but you will have to manually instanciate a Lifetime scope everywhere like this using(var scope1 = container.BeginLifetimeScope("myrequest")); I think is not so practical.

Obviously I suppose you will not use those elements outside of the request scope, or you will get an exception. In that case, you are forced to the MatchingLifetimeScope.

If you need more details, the Autofac guide is extremely clear.