Mediarion

An in-process mediator for CQRS on .NET, MIT licensed, shaped like MediatR so that moving an existing codebase is mostly a namespace change. No licence key, no dependencies.

public sealed class Ping : IRequest<string>
{
    public string Message { get; set; } = string.Empty;
}

public sealed class PingHandler : IRequestHandler<Ping, string>
{
    public Task<string> Handle(Ping request, CancellationToken cancellationToken) =>
        Task.FromResult("pong " + request.Message);
}

services.AddMediarion(cfg => cfg.RegisterServicesFromAssemblyContaining<Program>());

string answer = await sender.Send(new Ping { Message = "there" });

dotnet add package Mediarion
dotnet add package Mediarion.Extensions.DependencyInjection

Why this exists

MediatR 12.5.0 was the last release under plain Apache-2.0. From 13.0.0 the package is dual licensed — RPL-1.5 or a commercial licence — and asks for a licence key at run time. There is a free Community tier for organisations under five million dollars of revenue, which covers a lot of people and does not cover everybody, and which is a thing you now have to know about your employer before you can pick a library.

Version 12.5.0 stays Apache-2.0, because a licence already granted cannot be withdrawn. That line is frozen: no new features, no new target frameworks, no fixes.

Where it sits

martinothamar/Mediator already exists, is MIT, and is faster than this one. If you are on .NET 6 or later, are willing to write your handlers against a different set of interfaces, and speed is what you are choosing on, look at it first — the performance page includes it, and it wins.

What is missing, and what this is for: a mediator that is a drop-in — change the namespace and your handlers, behaviours and registrations compile as they are — that runs on .NET Framework 4.7.2 as well as .NET 10, and that carries no dependencies of its own.

Where to go next

  • Getting started — requests, notifications and the container.
  • Migrating from MediatR — what the drop-in claim is worth, and the one place the two libraries part company on purpose.
  • The pipeline — behaviours, pre- and post-processors, exception handlers, and the order they run in.
  • Streaming — IStreamRequest<T> and CreateStream, in a package of its own.
  • Ahead-of-time and the generator — how to publish an application with PublishAot.
  • Performance — the numbers, the runs they came from, and where this library loses.
  • API reference — every public type, generated from the XML documentation the build requires on each one.
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