Issue on Project with Mediator and MassTransit

[adamtrip]

When using Mediator on the same project with MassTransit I get the following error:

System.Exception: 'Invalid configuration detected for Mediator. Generated code for 'Singleton' lifetime, but got 'Scoped' lifetime from options. This means that the source generator hasn't seen the 'AddMediator' method call during compilation. Make sure that the 'AddMediator' method is called from the project that references the Mediator.SourceGenerator package.'

If I remove the MassTransit package and service registrations it all works just fine.

It only occurs in mediator 3.0.0-preview.X. If I downgrade to version 2.0.* the error does not happen.

EDIT: On version 2.1.6 also gives the same error

Thanks in advance!

[MustafaaYildirimmm]

Hello, I solved this;

I loaded Mediator.SourceGenerator and Mediator.Abstractions libraries into the API project and also the Mediator.Abstractions library into the project where commands and queries are located.

[jonmotos]

Same issue here, but with the elsa-core libraries

[martinothamar]

I think we would need a sample setup to identify the issues here. I'm a bit late to respond here but if you have something I'd apprecciate it

[diegomodolo]

Has anyone had success in solving this? I am getting this error when using Mediator and MassTransit in the same project.

[axel-zarate]

It happened to me too. If I call AddMasstransit and AddMediator in the same class (Program, Startup, etc.) I get the error. My solution was to move the call to AddMasstransit to an extension method on another file/class. It can be in the same project, but I ended up moving it down to my application layer project.

public static class ServiceRegistrationExtensions
{
    public static IServiceCollection AddApplicationServices(this IServiceCollection services)
    {
        services.AddMassTransit(options => ...);
        // Other registrations
    }
}

[adamtrip]

Sorry for the late reply. I ended up solving this by calling the MediatorExtension directly. Something like this:

var builder = WebApplication.CreateBuilder(args);

MediatorDependencyInjectionExtensions.AddMediator(builder.Services);

I'm not sure if this still works since I ended up not using MassTransit in the future and no longer had this issue

[TimothyMakkison]

I think I've reproduced this issue see #169. It appears to work when AddMediator() is called but produces the error when a configuration function is used.

On an unrelated note is the documentaion incorrect? DefaultServiceLifetime doesn't appear to exist.

[TimothyMakkison]

After a bit more testing I discovered that I can cause the exception just by adding using MassTransit;. I wonder if the compile time code that reads the AddMediator configuration is broken by a MassTransit type.

builder.Services.AddMediator(options => { }); is normally okay, adding the reference to MassTransit prevents this from compiling with the following error:

// Uncommenting this causes the exception
// using MassTransit;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddMediator(options =>
{
    options.Namespace = "SimpleConsole.Mediator";
    options.ServiceLifetime = ServiceLifetime.Transient;
});

// builder.Services.AddMassTransit();

var app = builder.Build();

app.MapGet("/", () => "Hello Mediator and MassTransit!");

app.Run();

EDIT: Both Elsa Core and MassTransit have an extension method called AddMediator See here

I suspect the code that reads the configuration at compile time see the AddMediator call as a call to Elsa core or Masstransit disregarding it. Then at runtime the mediator verfircation code runs, determines that the configuration wasn't read at compile time, throwing the exception.

I wonder if this could be fixed by passing the mediator extension method to Compilation. This code is emitted by the generator and therefore does not exist yet at compile time.

[martinothamar]

I wonder if this could be fixed by passing the mediator extension method to Compilation

What do you mean by this? You're right in that CompilationAnalyzer only looks at syntax and actually expects to not be able to resolve the invocation to a symbol (as that would indicate that the method belongs to some other library). So there's clearly been similar problems before, not sure what makes this different

[TimothyMakkison]

Can't remember if I wrote this anywhere but:

I think this is caused by MassTransit and elsa containing similar AddMediator methods to Mediator.
In the case of MassTransit, by referencing this library in the same file as our call to AddMediator, the C# compiler will think that AddMediator is a call to MassTransit.DependencyInjectionRegistrationExtensions.AddMediator. This causes Mediator.CompilationAnalyzer.ProcessAddMediatorConfiguration to not read the configuration anymore, as the ISymbol is no longer null (its usually null as the Compilation doesn't know about code it emits) and now has an unrecognised ContainingType of "MassTransit.DependencyInjectionRegistrationExtensions".

If my understanding is correct this would not be a problem for a normal library as the compiler/ide would detect that the AddMediator call has two conflicting methods and that the types cannot be inferred. This would be rectified by the user qualifying which method they intended to use. I suspect that because Mediator emits AddMedaitor the compiler/ide doesnt do the usual warning and assumes you meant to use MassTransit / Elsa.

In short; if this error occurs simply qualify the method call Mediator.AddMediator or specify the type parameter AddMediator((MediatorOption option) => .... This should prevent the error.

I don't know how to prevent this from happening. If my theory is correct, concretely defining the extension method alongside IMediator would prevent this. Of course this wouldn't have the source generated setup code so this library would not work 😞

It might be possible to write an analyzer which detects a possibly conflicting AddMediator call. I imagine this would be a lot of work with lots of edge cases. I'd settle with updating the documentation to mention this error

I wonder if this could be fixed by passing the mediator extension method to Compilation

I naively hoped that by parsing and adding the AddMediator method to _context.Compilation we'd be able to either detect a conflict or the compilation would magically figure out which call we wanted to use. This is not the case 😅

[martinothamar]

Looked into this myself as well, yeah this is just a simple ambiguous call and it doesn't really have anything to do with the source generator IMO. So yeah I agree the doc update should be sufficient here, the compiler error tells us what is wrong. The compiler is able to disambiguate if one does

• AddMediator(options => options.ServiceLifetime = ServiceLifetime.Singleton) - if the other candidate overload doesn't have ServiceLifetime
• AddMediator((MediatorOptions options) => {})

Closing this as I don't think there is much to do. I am adding a MassTransit sample here: #201