Resolving a dependency at runtime that uses InstancePerRequest service

[Eranga Abeysinghe]

Hi All,

I have a asp.net mvc app with entity framework where there should be only 1 DataContext per request.

In the Global.aspx.cs I have following code to register dependencies

            var builder = new ContainerBuilder();

            builder.RegisterType<DataContext>().InstancePerHttpRequest();

  Data.Controller.Instance.Container = builder.Build();

And in the other assembly I have

public abstract class EFRepository<TEntity> : IRepository<TEntity>

{

public EFRepository(DataContext dataContext)

{

} 

 

}

public abstract class Entity

{

//other stuff

        protected TRepository GetRepository<TRepository>()

        {

            return Controller.Instance.Container.Resolve<TRepository>();

        }

}

So when ever I want to call GetRepository method I get the following error {"No scope matching the expression 'value(Autofac.Builder.RegistrationBuilder`3+<>c__DisplayClass0[Em.Mdm.Data.DataContext,Autofac.Builder.ConcreteReflectionActivatorData,Autofac.Builder.SingleRegistrationStyle]).lifetimeScopeTag.Equals(scope.Tag)' is visible from the scope in which the instance was requested."} System.Exception {Autofac.Core.DependencyResolutionException}

Please advice as to how this can be avoided. Any changes I need to do are also welcome.

Thank You.

[Alex Meyer-Gleaves]

Hi Eranga,

Make sure you have registered the appropriate modules and made the required code changes to make the per request lifetime scope available.

http://code.google.com/p/autofac/wiki/MvcIntegration

If you are going to access the container directly (which you should avoid if possible) you will need to access the current lifetime scope using the IContainerProviderAccessor interface.

IContainerProviderAccessor accessor = (IContainerProviderAccessor)HttpContext.Current.ApplicationInstance;

ILifetimeScope lifetimeScope = accessor.ContainerProvider.RequestLifetime;

It would be better to inject the repository instances into your controllers instead though.

Cheers,

Alex.

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[Eranga Abeysinghe]

Hi Alex,

Thank you for helping me out but I was unable to incorporate your solution.

I am using asp.net MVC 3 so 'IContainerProviderAccessor' is not available.(is there a way to retrieve this?)

As you said Repositories are injected to Controllers. But there are cases where an entity needs to access another entity through the repository or custom lazy loading scenario where I need an instance of the repository.

Additional info.

The entities and UI reside on different assemblies.

Can not control entity creation part since entity framework is creating the entities. (So unable to inject into entities)

Please help.

Thanks & Regards,

Eranga

[Alex Meyer-Gleaves]

Hi Eranga,

If you are using MVC 3 you will need to compile from source. MVC 3 support will be included in the upcoming Autofac 2.4 release. The link below will help you get started with the MVC 3 integration. 

http://code.google.com/p/autofac/wiki/Mvc3Integration

You no longer need to add the modules to your configuration file or implement the IContainerProviderAccessor interface. Follow the instructions in the "Upgrading from ASP.NET MVC 2" section of the documentation to undo any changes you added by following the previous instructions.

I had wondered about what version you were using but assumed it was MVC 2 because the MVC 3 support had not been released yet. Sorry about the confusion.

Cheers,

Alex.

--

[Eranga Abeysinghe]

Hi Alex,

Thanks for the reply and sorry for not specifying that I use MVC3. Good to hear that 2.4 is coming soon. I already compiled the source and using it. For the common cases its working great.

My problem is how to resolve a dependency at runtime in another assembly which uses a dependency registered as InstancePerRequest in another assembly.

Say in my UI project(Global.aspx.cs) I have

             var builder = new ContainerBuilder();

            builder.RegisterType<DataContext>().InstancePerHttpRequest();

  Data.Controller.Instance.Container = builder.Build();

And In my Data project I have 

public abstract class EFRepository<TEntity> : IRepository<TEntity>
{

public EFRepository(DataContext dataContext)

{

} 

 

}
public abstract class Entity
{
//other stuff
        protected TRepository GetRepository<TRepository>()
        {
            return Controller.Instance.Container.Resolve<TRepository>();
        }

}

 

public class Item : Entity

{

internal void OnBeforeInsert()

{

var categoryRepository = GetRepository<ICategoryRepository>();

//other stuff 

} 

}

 

So inorder to use the container created in the UI project I used a Singleton to access the container in the Data Project. (Highlighted in bold)

The container is used as highlighted in Blue. But when I access that (Highlighted in Red) I get the following error.

{"No scope matching the expression 'value(Autofac.Builder.RegistrationBuilder`3+<>c__DisplayClass0[Em.Mdm.Data.DataContext,Autofac.Builder.ConcreteReflectionActivatorData,Autofac.Builder.SingleRegistrationStyle]).lifetimeScopeTag.Equals(scope.Tag)' is visible from the scope in which the instance was requested."} System.Exception {Autofac.Core.DependencyResolutionException}

Please help me out. I do not have a deep knowledge of Autofac. I hope you can understand my problem better now.

If the design is flowed (can this be done without the Singleton) please advice.

Thanks & Regards,

Eranga

[Nicholas Blumhardt]

Hi Eranga,

Instead of InstancePerHttpRequest() use InstancePerLifetimeScope(). This will work in both cases.

Cheers,

Nick

Thanks & Regards,

Eranga

--

[era...@gmail.com]

Hi Nick,

Thanks for your reply. Found an alternate solution when I went through the source of 'AutofacDependencyResolver'. I access the 'RequestLifetimeScope' property through a delegate from my 'Data' project.

I will try your solution also. Thanks again for helping me out.

Thanks & Regards,

Eranga

[bala....@gmail.com]

Hi,

I to had the same problem, how did you resolve that datacontext
Can you send code are same link.