Autofac 无法解析 DbContext

Question

I am receiving this error message from Autofac;:

None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'MyService`1[MyContext]' can be invoked with the available services and parameters: Cannot resolve parameter 'MyContext context' of constructor 'Void .ctor(MyContext)'.

The error occurs on this line of code (also shown in the code below):

IMyService myService = container.Resolve<IMyService>();  // error here

I am interested to note that when I include this line in my registrations, everything works:

builder.RegisterSource(new AnyConcreteTypeNotAlreadyRegisteredSource());

The fact that it all works when I register AnyConcreteType... leads me to believe I am not not registering something. My question is what am I not registering? The error message appears to name MyContext as the culprit but clearly I am registering it as shown below.
I really dont want to use the AnyConcreteType... catch all because I want to explicity register only the the classes I need.

My service is constructed like this:

public class MyService<T> : BaseService<T>, IMyService where T:DbContext,IMyContext
{
    public MyService(T context) : base(context)
    {
    }
}

MyService derives from BaseService:

public abstract class BaseService<T> : IDisposable where T:DbContext, IMyContext
{
    internal T db;

    public BaseService(T context)
    {
        db = context;
    }
}

MyContext is passed to MyService and is constructed like this:

public partial class MyContext : DbContext, IMyContext
{
    public MyContext(INamedConnectionString conn)
        : base(conn.ConnectionString)
    {
        Configuration.ProxyCreationEnabled = false;
    }
}

Here is NamedConnectionString

public class NamedConnectionString : INamedConnectionString
{
    public string ConnectionString { get; set; }
}

Here is how I register the above:

builder.RegisterType<MyService<MyContext>>().As<IMyService>();  
builder.RegisterType<NamedConnectionString>().As<INamedConnectionString>().SingleInstance();
builder.RegisterType<MyContext>().As<IMyContext>().InstancePerLifetimeScope();
builder.RegisterType<DbContext>(); // is this necessary??

And here is how I call it:

    var container = builder.Build();
    DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
    INamedConnectionString namedConnectionString = container.Resolve<INamedConnectionString>();
    namedConnectionString.ConnectionString = myConnectionString;
    IMyService myService = container.Resolve<IMyService>();  // error here

Answer 1

Autofac and ASP .Net MVC 4 Web API

The above thread is related. It does not answer the question but it helped me start troubleshooting in the right direction. The solution is here:

I removed these two lines:

builder.RegisterType<MyContext>().As<IMyContext>().InstancePerLifetimeScope();
builder.RegisterType<DbContext>(); // is this necessary??

and replaced them with this one:

builder.RegisterType<MyContext>().InstancePerLifetimeScope();

Answer 2

This worked for me

builder.RegisterType().As().InstancePerLifetimeScope();

Answer 3

Got this working by using builder.RegisterType<InventoryContext>().InstancePerLifetimeScope();.

Context:

I have a DBContext class, I have services that injects the Context and then have Controllers to call the Services (Interface).

And then on global.asax, called the builder.RegisterType<InventoryContext>().InstancePerLifetimeScope(); . This worked well, been a while since I worked with an MVC project again.

If there's anyone having issues with this you can refer to this again.