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Autofac not resolving interfaces in other project

I'm trying to write a generic command bus (Part of class library) that uses different commands and handlers in each of my services.
The following code produces the following exception:
System.Exception: Command does not have any handler RegisterUserCommand
I was under the impression passing the the ExecutingAssemblies of my UserService would allow the Container to resolve the handler in my UserService but apparently not.
Am I doing something wrong?
CommandBus:
public interface ICommandBus
{
void Send<T>(T Command) where T : ICommand;
}
public class CommandBus : ICommandBus
{
private IContainer Container { get; set; }
public CommandBus(Assembly assembly)
{
Container = new CommandBusContainerConfig().Configure(assembly);
}
public void Send<TCommand>(TCommand command) where TCommand : ICommand
{
var handlers = Container.Resolve<IEnumerable<ICommandHandler<TCommand>>>().ToList();
if (handlers.Count == 1)
{
handlers[0].Handle(command);
}
else if (handlers.Count == 0)
{
throw new System.Exception($"Command does not have any handler {command.GetType().Name}");
}
else
{
throw new System.Exception($"Too many registred handlers - {handlers.Count} for command {command.GetType().Name}");
}
}
}
ContainerBuilder:
public class CommandBusContainerConfig : IContainerConfig
{
public IContainer Configure(Assembly executingAssembly)
{
var builder = new ContainerBuilder();
builder.RegisterAssemblyTypes(executingAssembly)
.Where(x => x.IsAssignableTo<ICommandHandler>())
.AsImplementedInterfaces();
builder.Register<Func<Type, ICommandHandler>>(c =>
{
var ctx = c.Resolve<IComponentContext>();
return t =>
{
var handlerType = typeof(ICommandHandler<>).MakeGenericType(t);
return (ICommandHandler)ctx.Resolve(handlerType);
};
});
return builder.Build();
}
}
In my UserService(ASP.Net Core 3), which is a different project that references the above CommandBus:
public class RegisterUserCommand : ICommand
{
public readonly string Name;
public readonly Address Address;
public string MobileNumber;
public string EmailAddress;
public RegisterUserCommand(Guid messageId, string name, string mobileNumber, string emailAddress, Address address)
{
Name = name;
Address = address;
MobileNumber = mobileNumber;
EmailAddress = emailAddress;
}
CommandHandler:
public class RegisterUserComnmandHandler : ICommandHandler<RegisterUserCommand>
{
public void Handle(RegisterUserCommand command)
{
Console.WriteLine($"Create user {command.Name} {command.MobileNumber} - handler");
}
}
Startup:
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<ICommandBus>(new CommandBus(Assembly.GetExecutingAssembly()));
}
Controller:
private readonly ICommandBus _commandBus;
public UsersController(ICommandBus commandBus) {
_commandBus = commandBus;
}
// POST api/values
[HttpPost]
public async Task<IActionResult> Post([FromBody]RegisterUserCommand command)
{
if (ModelState.IsValid)
{
CommandBus commandBus = new CommandBus(Assembly.GetExecutingAssembly());
commandBus.Send(command);
_commandBus.Send(Command); //Same result as above
// return result
return Ok(command);
}
return BadRequest();
}
Thanks,

The main error is here :
builder.RegisterAssemblyTypes(executingAssembly)
.Where(x => x.IsAssignableTo<ICommandHandler>())
.AsImplementedInterfaces();
RegisterUserComnmandHandler is not a ICommandHandler but a ICommandHandler<RegisterUserCommand>. Instead of IsAssignableTo<> method you can use the IsClosedTypeOf which is an Autofac extension which do exactly what you can.
builder.RegisterAssemblyTypes(executingAssembly)
.Where(x => x.IsClosedTypeOf(typeof(ICommandHandler<>)))
.AsImplementedInterfaces();
By the way, in your code sample you are using another Container. Most of the time it is always simple to have a single container for the whole application. To get things organised you can use autofac module. You are also resolving straight from the container and not using scope this means that your instance graph won't be disposed at the end of the operation but will stay for the whole lifetime of the container.
In your controller, I saw that you are building a new CommandBus for each request, which will create a new container. Building a new container is a heavy operation and you should avoid doing it often but only once of the startup of the application.
Also I don't get the point of this registration :
builder.Register<Func<Type, ICommandHandler>>(c =>
{
var ctx = c.Resolve<IComponentContext>();
return t =>
{
var handlerType = typeof(ICommandHandler<>).MakeGenericType(t);
return (ICommandHandler)ctx.Resolve(handlerType);
};
});
It doesn't looks you need it and it seems useless to me

This took me a while to figure out. But my CommandHandler interface was incorrectly defined. It should look like:
public interface ICommandHandler { }
public interface ICommandHandler<T> : ICommandHandler where T : ICommand
{
void Handle(T command);
}
}
When trying to resolve the CommandHandler in the Autofac configuration class, the .Where(x => x.IsAssignableTo<ICommandHandler>()) was failing because the class was assignable to ICommandHandle<T> not ICommandHandler

ASP.NET Core API, Mediatr send method raises exception unable to resolve service for type

I have a ASP.NET Core API, where I am trying to use FluentValidation with Mediatr.
Currently when the controller method is attempting to call Send on the mediatr instance it generates:
Exception thrown: 'System.InvalidOperationException' in
Microsoft.Extensions.DependencyInjection.dll: 'Unable to resolve
service for type 'GetApplicationQuery' while attempting to activate
'GetApplicationQueryValidator'.'
The query, validator and response class look like this:
public class GetApplicationQuery : IRequest<Response>
{
private string _name;
public GetApplicationQuery(string name)
{
_name = name;
}
public string Name { get { return _name; } }
}
public class GetApplicationQueryHandler : IRequestHandler<GetApplicationQuery, Response>
{
public GetApplicationQueryHandler() { }
public async Task<Response> Handle(GetApplicationQuery request, CancellationToken cancellationToken)
{
return new Response("yadda yadda");
}
}
public class GetApplicationQueryValidator : AbstractValidator<GetApplicationQuery>
{
public GetApplicationQueryValidator(GetApplicationQuery request)
{
RuleFor(m => m.Name).MinimumLength(30).WithMessage("Name must be greater than 30 characters, long");
}
}
public class Response
{
private readonly IList<string> _messages = new List<string>();
public IEnumerable<string> Errors { get; }
public object Result { get; }
public Response() => Errors = new ReadOnlyCollection<string>(_messages);
public Response(object result) : this() => Result = result;
public Response AddError(string message)
{
_messages.Add(message);
return this;
}
}
The configuration I have in the Startup class looks like this:
public void ConfigureServices(IServiceCollection services)
{
AddMediatr(services);
services.AddMvc().AddFluentValidation(fv =>
{
fv.RegisterValidatorsFromAssemblyContaining<Startup>();
fv.RunDefaultMvcValidationAfterFluentValidationExecutes = false;
}).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
}
private static void AddMediatr(IServiceCollection services)
{
const string applicationAssemblyName = "ApplicationApi";
var assembly = AppDomain.CurrentDomain.Load(applicationAssemblyName);
AssemblyScanner
.FindValidatorsInAssembly(assembly)
.ForEach(result => services.AddScoped(result.InterfaceType, result.ValidatorType));
services.AddScoped(typeof(IPipelineBehavior<,>), typeof(ValidatorHandler<,>));
services.AddMediatR(assembly);
}
I am guessing I have the configuration wrong but I have been changing configuration several times with no success.
Any guidance would be much appreciated

GetApplicationQueryValidator is taking GetApplicationQuery as a constructor dependency but the collection doesn't know about it to be able to inject it.
Also not seeing how it is to be used in that validator. I would suggest removing GetApplicationQuery from the constructor since it doesn't look like it is needed.
public class GetApplicationQueryValidator : AbstractValidator<GetApplicationQuery> {
public GetApplicationQueryValidator() {
RuleFor(m => m.Name).MinimumLength(30).WithMessage("Name must be greater than 30 characters, long");
}
}

Single Message Handler Factory using Autofac

So I have a marker interface called IMessage.Then I have classes like:
public class MessageA: IMessage
{
}
Then I have message handlers defined as:
internal interface IMessageHandler<in T> where T: IMessage
{
void Handle(T message);
}
public class MessageAHandler : IMessageHandler<MessageA>
{
public void Handle(T message)
{
//Some logic here
}
}
I want to re-route these messages that I get to the corresponding message handlers when I get a new message. Example:
public class MessageReceiver
{
public void ReceiveMessage(IMessage message)
{
//somehow resolve the appropiate message handler here
messageHandler.Handle(message);
}
}
I can accomplish this right now by using factories like below but I need to have a dependency on each a new factory per different type of message. So I'm wondering if there is a way to create a single factory that will be smart enough to resolve the appropiate message handler?
public class MessageReceiver
{
private readonly Func<IMessageHandler<MessageA>> _messageAFactory;
public MessageReceiver(Func<IMessageHandler<MessageA>> messageAFactory)
{
_messageAFactory= messageAFactory;
}
public void ReceiveMessage(IMessage message)
{
if (message is MessageA)
{
var messageHandler = _messageAFactory();
messageHandler.Handle(message as MessageA);
}
// Add more if-statements here for more messages
}
}
Autofac Registration
public class InfrastructureModule : Module
{
protected override void Load(ContainerBuilder builder)
{
//Register the types in the infrastructure assembly
builder.RegisterAssemblyTypes(ThisAssembly).AsImplementedInterfaces()
.InstancePerLifetimeScope();
//Register the message handlers
builder.RegisterAssemblyTypes(ThisAssembly)
.Where(x => x.IsAssignableFrom(typeof(IMessageHandler<IMessage>)))
.InstancePerDependency().AsImplementedInterfaces();
}
}

First I'll make a small implementation for your messages, just a basic handled flag, in order to test
public class MessageA : IMessage
{
public bool Handled
{
get;
private set;
}
public void MarkAsHandled()
{
this.Handled = true;
}
}
public class MessageB : IMessage
{
public bool Handled
{
get;
private set;
}
public void MarkAsHandled()
{
this.Handled = true;
}
}
Now let's implement both handlers as:
public class MessageAHandler : IMessageHandler<MessageA>
{
public void Handle(MessageA message)
{
message.MarkAsHandled();
}
}
public class MessageBHandler : IMessageHandler<MessageB>
{
public void Handle(MessageB message)
{
message.MarkAsHandled();
}
}
As a side note, you might want to mark your IMessageHandler interface as public (I get compiler error if visibility is set as internal).
Now let's add a small handler:
public interface IMessageHandler
{
Type MessageType { get; }
void Handle(IMessage message);
}
public class MessageHandlerAdapter<T> : IMessageHandler where T : IMessage
{
private readonly Func<IMessageHandler<T>> handlerFactory;
public MessageHandlerAdapter(Func<IMessageHandler<T>> handlerFactory)
{
this.handlerFactory = handlerFactory;
}
public void Handle(IMessage message)
{
var handler = handlerFactory();
handler.Handle((T)message);
}
public Type MessageType
{
get { return typeof(T); }
}
}
We can now implement MessageReceiver this way:
public class MessageReceiver
{
private readonly IEnumerable<IMessageHandler> handlers;
public MessageReceiver(IEnumerable<IMessageHandler> handlers)
{
this.handlers = handlers;
}
public void ReceiveMessage(IMessage message)
{
var handler = this.handlers.Where(h => h.MessageType == message.GetType()).FirstOrDefault();
if (handler != null)
{
handler.Handle(message);
}
else
{
//Do something here, no handler found for message type
}
}
}
Now to test that our messages are processed properly, here is a small test:
[TestClass]
public class TestSelector
{
private IContainer container;
[TestMethod]
public void TestMethod()
{
var processor = container.Resolve<MessageReceiver>();
MessageA ma = new MessageA();
MessageB mb = new MessageB();
processor.ReceiveMessage(ma);
processor.ReceiveMessage(mb);
Assert.AreEqual(ma.Handled, true);
Assert.AreEqual(mb.Handled, true);
}
}
And we need to modify registration a bit, if opting for manual registration, we do as follow:
public TestSelector()
{
var containerBuilder = new ContainerBuilder();
containerBuilder.RegisterType<MessageAHandler>().As<IMessageHandler<MessageA>>();
containerBuilder.RegisterType<MessageBHandler>().As<IMessageHandler<MessageB>>();
containerBuilder.RegisterType<MessageHandlerAdapter<MessageA>>().As<IMessageHandler>();
containerBuilder.RegisterType<MessageHandlerAdapter<MessageB>>().As<IMessageHandler>();
containerBuilder.RegisterType<MessageReceiver>();
this.container = containerBuilder.Build();
}
In here, we now need to register one handler and the relevant adapter.
It is also of course possible to perform assembly scan, but this requires a little bit more plumbing, since using:
builder.RegisterAssemblyTypes(ThisAssembly)
.Where(x => x.IsAssignableFrom(typeof(IMessageHandler<IMessage>)))
.InstancePerDependency().AsImplementedInterfaces();
will not work
typeof(MessageAHandler).IsAssignableFrom(typeof(IMessageHandler<IMessage>))
will return false, since MessageAHandler implements IMessageHandler, not IMessageHandler
To do automatic discovery and registration, here is a snippet:
public TestSelector()
{
var containerBuilder = new ContainerBuilder();
Func<Type, Type> GetHandlerInterface = (t) => t.GetInterfaces()
.Where(iface => iface.IsGenericType && iface.GetGenericTypeDefinition() == typeof(IMessageHandler<>)).FirstOrDefault();
var handlerTypes = typeof(IMessage).Assembly.GetTypes()
.Where(type => type.IsClass
&& !type.IsAbstract
&& GetHandlerInterface(type) != null);
foreach (Type handlerType in handlerTypes)
{
Type messageType = GetHandlerInterface(handlerType).GetGenericArguments()[0];
var genericHandler = typeof(MessageHandlerAdapter<>).MakeGenericType(messageType);
containerBuilder.RegisterType(handlerType).AsImplementedInterfaces();
containerBuilder.RegisterType(genericHandler).As<IMessageHandler>();
}
containerBuilder.RegisterType<MessageReceiver>();
this.container = containerBuilder.Build();
}

For anyone who is still looking for better solution for auto dispatching to appropriate message handlers registered, there is a nice implementation via MediatR.This is awesome library which can dispatch messages to appropriate registered handlers, and has capability to post messages to multiples handlers.
It is best suited for CQRS scenarios and also for Async Web API, refer CQRS using MediatR . There is a nice support when using DI container like Autofac and StructuredMap, Refer to wiki page of MediatR wiki for full details on DI support.

NServiceBus.IStartableBus is not registered in the container. NServiceBus 4.6.3

I am attempting a very simple application with NServiceBus and Ninject.
I am attempting to use Ninject as the container for NServiceBus, but I am getting the following error - "NServiceBus.IStartableBus is not registered in the container."
I'm sure the answer is quite obvious... just not to me!
My code is as follows
public class StartApp : IWantCustomInitialization, IWantToRunWhenBusStartsAndStops
{
private static IKernel _kernel;
public IBus Bus { get; set; }
public void Init()
{
Configure.Serialization.Json();
}
public void Start()
{
_kernel = new StandardKernel();
Configure.With()
.NinjectBuilder(_kernel)
.CreateBus()
.Start();
Bus.Send(new TestMessage {Id = Guid.NewGuid(), MessageText = "Bloop"});
}
public void Stop()
{
}
}
namespace NServiceBus_Ninject_Simple
{
public class EndpointConfig : IConfigureThisEndpoint, AsA_Server
{ }
}

This google groups discussion is about the same issue.
It seems you are creating the configuration in the wrong place.
It should look like this:
public abstract class DefaultEndpointConfig
: IConfigureThisEndpoint
, IWantCustomInitialization
{
IWantCustomInitialization.Init()
{
Configure
.With()
.NinjectBuilder();
// + any other config;
// Call optional endpoint specific config
Init();
}
public virtual void Init()
{
}
}
See here (Johannes Gustafsson)
It needs to be done in the EndPoint-Configuration (for every endpoint, this is why he suggests using a base class) and it needs to implement IConfigureThisEndpoint.

Using Autofac with Dynamic Proxy that output message automatic

public interface ILog
{
void Write(string msg);
}
public class MyLog : ILog
{
public void Write(string msg)
{
Console.WriteLine(msg);
}
}
public interface ICanLog
{
ILog Log { get; set; }
}
public interface IMyClass
{
void Test();
}
public class MyClass : IMyClass, ICanLog
{
public ILog Log { get; set; }
public void Test()
{
Log.Write("Test");
}
}
I am using Autofac with Castle DynamicProxy,
and try to let MyClass Test Method output "BEGIN"/"END" automatic.
public class MyLogInterceptor : IInterceptor
{
public void Intercept(IInvocation invocation)
{
Console.WriteLine("BEGIN");
invocation.Proceed();
Console.WriteLine("END");
}
}
The following is test code:
ContainerBuilder builder = new ContainerBuilder();
builder.RegisterType<MyLog>().As<ILog>();
builder.Register(c =>
{
ProxyGenerator g = new ProxyGenerator();
object proxy = g.CreateClassProxy(typeof(MyClass), new MyLogInterceptor());
ICanLog proxyICanLog = (ICanLog)proxy;
proxyICanLog.Log = c.Resolve<ILog>();
return proxy;
}).As<IMyClass>();
using (var container = builder.Build())
{
objectContext.Container = container;
IMyClass myclass = container.Resolve<IMyClass>();
myclass.Test();
}
But result no output "BEGIN"/"END", why ?
and if I create AutoLogModule that try build Log Property Instance automatic
public class AutoLogModule : Autofac.Module
{
protected override void AttachToComponentRegistration(IComponentRegistry componentRegistry, IComponentRegistration registration)
{
var type = registration.Activator.LimitType;
if (HasPropertyDependencyOnClass(type))
{
registration.Activated += InjectClassViaProperty;
}
}
private bool HasPropertyDependencyOnClass(Type type)
{
return type.GetProperties().Any(property => property.CanWrite && property.PropertyType==typeof(ILog));
}
private void InjectClassViaProperty(object sender, ActivatedEventArgs<object> evt)
{
var type = evt.Instance.GetType();
var propertyInfo = type.GetProperties().First(x => x.CanWrite && x.PropertyType==typeof(ILog));
ILog log = new MyLog();
propertyInfo.SetValue(evt.Instance, log, null);
}
}
The following is test code:
ContainerBuilder builder = new ContainerBuilder();
builder.RegisterType<MyLog>().As<ILog>();
builder.RegisterModule(new AutoLogModule());
builder.Register(c =>
{
ProxyGenerator g = new ProxyGenerator();
object proxy = g.CreateClassProxy(typeof(MyClass), new MyLogInterceptor());
//ICanLog proxyICanLog = (ICanLog)proxy;
//proxyICanLog.Log = c.Resolve<ILog>();
return proxy;
}).As<IMyClass>();
using (var container = builder.Build())
{
objectContext.Container = container;
IMyClass myclass = container.Resolve<IMyClass>();
myclass.Test();
}
The result is Test Method throw
"Object reference not set to an instance of an object."
in Log.Write("Test")
How to write this feature?

I know this is a rather old post but as I was trying to accomplish the same thing with Autofac and I found the documentation that helped me to achieve it. I will answer just in case it helps someone else.
In my case I'm using Autofac 4.92 and and extra package for DynamicProxy called Autofac.Extras.DynamicProxy 4.5.0 as the documentations sates.
I see a difference where you register your Interceptors. Even though what you are doing is what I would have done initially; is not what Autofac Documentation currently says about how to Register Interceptors:
builder.RegisterType<MyClass>().As<IMyClass>().EnableInterfaceInterceptors();
// Typed registration
builder.Register(c => new MyLogInterceptor ();
Lastly, you need to Associate Interceptors with Types to be Intercepted:
[Intercept(typeof(MyLogInterceptor))]
public class MyClass : IMyClass, ICanLog
{
public ILog Log { get; set; }
public void Test()
{
Log.Write("Test");
}
}
I hope this answer may help. In any case, the Autofac documentation explains step by step how to do it just in case my code may mistakenly skip some relevant part.