MediatorServiceCollectionExtensions

Namespace: RA.Utilities.Feature.Extensions

The MediatorServiceCollectionExtensions class registers the core IMediator service with the .NET dependency injection container and applies the compile-time handler registrations produced by the package's source generator.

It provides a simple, one-line extension method, AddMediator, that handles both:

// From: /RA.Utilities/Application/RA.Utilities.Feature/Extensions/MediatorServiceCollectionExtensions.cs

public static IServiceCollection AddMediator(this IServiceCollection services)
{
    HandlerRegistrations.ApplyAll(services);
    MediatorRegistrations.ApplyAll(services);
    return services;
}

Since v10.2.0 a source generator shipped in the package emits a module initializer for every assembly containing IRequestHandler<,> / IRequestHandler<> / INotificationHandler<> implementations. Those initializers queue DI registrations (request handlers scoped, notification handlers transient) which AddMediator() then applies — that is why plain handlers need no explicit AddFeature / AddNotification call. See the Auto Registration guide for the assembly-loading guarantee and diagnostics.

Since v11.1.0, the generator also emits the Mediator implementation of IMediator per assembly — the only mediator in the package. AddMediator() applies those registrations, so IMediator resolves to the generated implementation. See the Generated Mediator guide for the dispatch strategy and the message/handler diagnostics.

Why is this important?

1. Simplifies Setup:

It provides a clean, discoverable way for a developer using your library to get it working. Instead of needing to know the concrete implementation (Mediator), its correct lifetime (Scoped), or the auto-registration queue, they can simply call services.AddMediator().

2. Encapsulation:

It hides the implementation details of the mediator pattern. If you were to change the concrete Mediator class (or the registration mechanics) in the future, developers using your library wouldn't need to change their startup code as long as the extension method remains.

3. Foundation for Features:

This registration is the foundation upon which all other features from RA.Utilities.Feature are built. The source generator and the fluent builders (.AddFeature(), .AddNotification()) register the handlers and behaviors, while AddMediator registers the central "dispatcher" that actually processes the requests and notifications — and applies the auto-discovered handlers.

In short, this class is the essential bootstrapping step required to use the CQRS pattern provided by the RA.Utilities.Feature library.