MediatR in Azure Function v4

Question

I decided to use MediatR in my Azure Function app. I downloaded MediatR v12.1.1 in my Azure Function project. I have dependent project(class library) with name Services where I have queries(which implement IRequest) and handlers (which implement IRequestHandler<TRequest, TResult>). I added the following rows in Startup.cs of Azure Function project:

 public override void Configure(IFunctionsHostBuilder builder)
        {
    builder.Services.AddMediatR(cfg =>
            {
                cfg.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly());
            });
    }

My Function:

 public class SomeName
    {
        private readonly IMediator _mediator;

        public SomeName(IMediator mediator)
        {
            _mediator = mediator;
        }

        [FunctionName("SomeName")]
        public async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            var tokenString = req.Query["token"];
            var token = Guid.Parse(tokenString);
            var query = new GetUserDetail(token);
            var result = await _mediator.Send(query);
            return result != null ? new OkObjectResult(result) : new NotFoundResult();
        }
    }

As DI Container I use Autofac. When I run my function I get the following error:

System.Private.CoreLib: Exception while executing function: SomeName. Autofac: The requested service 'MediatR.IRequestHandler`2[Some_info]' has not been registered. To avoid this exception, either register a component to provide the service, check for service registration using IsRegistered(), or use the ResolveOptional() method to resolve an optional dependency.

How can I fix that error?

Answer 1

Assembly.GetExecutingAssembly() returns assembly that contains your functions. Mediatr scans it for types that imlement IRequestHandler<,> interface. Since you have commands and queries in dependant project, this assembly scan results in 0 types found. This means you need to pass different assembly.

You may try to register it via RegisterServicesFromAssemblyContaining<AnyTypeFromYourOtherProject>() where AnyTypeFromYourOtherProject is a type from this project that contains your requests

Example

.AddMediatR(cfg =>
{
    cfg.RegisterServicesFromAssemblyContaining<Class1>();
});

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