Error after Removing Mediatr and Adding Mediator.. Issue in the wiring up.

[vijayphani]

        // Register MediatR
        services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly()));

        Commented the above line added a new line 

        services.AddMediator();

       Below is the error. 

fail: Cpa.Fas.ProductMs.WebApi.Middleware.ExceptionHandlingMiddleware[0]
An unhandled exception occurred: No handler registered for message type: Cpa.Fas.ProductMs.Application.Products.Commands.CreateProduct.CreateProductCommand
Mediator.MissingMessageHandlerException: No handler registered for message type: Cpa.Fas.ProductMs.Application.Products.Commands.CreateProduct.CreateProductCommand
at Mediator.Mediator.ThrowMissingHandler(Object msg) in C:\Source\fas-product-ms\src\core\Cpa.Fas.ProductMs.Domain\obj\Debug\net8.0\Mediator.SourceGenerator\Mediator.SourceGenerator.IncrementalMediatorGenerator\Mediator.g.cs:line 1077
at Mediator.Mediator.ThrowInvalidRequest[T](T msg, String paramName) in C:\Source\fas-product-ms\src\core\Cpa.Fas.ProductMs.Domain\obj\Debug\net8.0\Mediator.SourceGenerator\Mediator.SourceGenerator.IncrementalMediatorGenerator\Mediator.g.cs:line 1102
at Mediator.Mediator.Send[TResponse](IRequest1 request, CancellationToken cancellationToken) in C:\Source\fas-product-ms\src\core\Cpa.Fas.ProductMs.Domain\obj\Debug\net8.0\Mediator.SourceGenerator\Mediator.SourceGenerator.IncrementalMediatorGenerator\Mediator.g.cs:line 846 at Cpa.Fas.ProductMs.WebApi.Controllers.ProductsController.CreateProduct(CreateProductRequestViewModel request) in C:\Source\fas-product-ms\src\presentation\Cpa.Fas.ProductMs.WebApi\Controllers\ProductsController.cs:line 38 at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask1 actionResultValueTask)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Program.<>c.<<

$>b__0_3>d.MoveNext() in C:\Source\fas-product-ms\src\presentation\Cpa.Fas.ProductMs.WebApi\Program.cs:line 73
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.HttpLogging.HttpLoggingMiddleware.InvokeInternal(HttpContext context, HttpLoggingOptions options, HttpLoggingAttribute loggingAttribute, HttpLoggingFields loggingFields)
at Microsoft.AspNetCore.HttpLogging.HttpLoggingMiddleware.InvokeInternal(HttpContext context, HttpLoggingOptions options, HttpLoggingAttribute loggingAttribute, HttpLoggingFields loggingFields)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Cpa.Fas.ProductMs.WebApi.Middleware.ExceptionHandlingMiddleware.InvokeAsync(HttpContext httpContext) in C:\Source\fas-product-ms\src\presentation\Cpa.Fas.ProductMs.WebApi\Middleware\ExceptionHandlingMiddleware.cs:line 20

[vijayphani]

I added this too.. Still the same error

builder.Services.AddMediator(options =>
{
options.ServiceLifetime = ServiceLifetime.Singleton; // Use Scoped lifetime for MediatR services
});

[mrmyroll2]

Sorry if I’m mistaken, but are your handler and controller in the same .csproj?
Based on my experience, if you’re following Clean Architecture and your controllers are in a different project from your application (where the handlers are), the handlers might not be generated. I’ve tried this in a simpler setup where both controllers and handlers are in the same project, and it worked fine. The issue could be related to having them in separate projects.
Give it a try—just sharing my experience, but I could be wrong.

[martinothamar]

I'm not sure what could be wrong here as I have no insight into the project setup here. You could take a look at some samples in this repo to see if you can spot the issue or you can post a repro if you would like more help

[ISAF87]

A small insight in my process, which might aid someone with a similar issue
Just went through a similar process in our webAPI.

Our project structure looks something like this:

• WebApi
• DIConfiguration
• Business logic (handlers etc)
• Business Interfaces
• Data (repos)
• Data Interfaces
• DataDIConfiguration

I installed the Mediator.SourceGenerator nuget package in the webapi project as per the documentation.

services.AddMediator(cfg =>
{
cfg.ServiceLifetime = ServiceLifetime.Transient;
cfg.Assemblies = [typeof(SomeRequestHandlerHandler)]; // remove this to go through all references
});

We have a unit test which validates whether it can resolve all interfaces from the collection, which failed, unable to resolve any handler.
I removed the cfg.Assemblies line later, as the documentation states that it will go through ALL referenced assemblies.
After this change it was able to resolve the handlers.

This can also be validated by looking at the generated code in:

[project where sourcegenerator is installed] -> Dependencies -> Analyzers -> Mediator.SourceGenerator -> Mediator.g.cs.

Hope this helps