Shuttle.Core.Mediator

PM> Install-Package Shuttle.Core.Mediator

The Shuttle.Core.Mediator package provides a mediator pattern implementation.

Configuration

In order to get all the relevant bits working you would need to register the IMediator dependency along with all the relevant IParticipant (for synchronous Send), or IAsyncParticipant (for asynchronous SendAsync), dependencies.

You can register the mediator using IServiceCollection:

services.AddMediator(builder =>
{
    builder.AddParticipants(assembly);
    builder.AddParticipant<Participant>();
    builder.AddParticipant(participantType)
    builder.AddParticipant<Message>(participant)
});

IMediator

The core interface is the IMediator interface and the default implementation provided is the Mediator class.

This interface provides a synchronous calling mechanism and all participant implementations need to be thread-safe singleton implementations that are added to the mediator at startup. Any operations that require transient mechanisms should be handled by the relevant participant.

void Send(object message, CancellationToken cancellationToken = default);

The Send method will find all participants that implement the IParticipant<T> with the type T of the message type that you are sending.

Task SendAsync(object message, CancellationToken cancellationToken = default);

The SendAsync method will find all participants that implement the IAsyncParticipant<T> with the type T of the message type that you are sending.

Participants that are marked with the BeforeParticipantAttribute filter will be executed first followed by all participants with no filter attributes and then finally all participants marked with the AfterParticipantAttribute filter will be called.

Participants

public interface IAsyncParticipant<in T>
{
    Task ProcessMessageAsync(IParticipantContext<T> context);
}

public interface IParticipant<in T>
{
    void ProcessMessage(IParticipantContext<T> context);
}

A participant would handle the message that is sent using the mediator. There may be any number of participants that process the message.

Design philosophy

There are no request/response semantics and the design philosophy here is that the message encapsulates the state that is passed along in a pipes & filters approach.

However, you may wish to make use of one of the existing utility classes:-

RequestMessage<TRequest>

The only expectation from a RequestMessage<TRequest> instance is either a success or failure (along with the failure message).

RequestResponseMessage<TRequest, TResponse>

The RequestResponseMessage<TRequest, TResponse> takes an initial TRequest object and after the mediator processing would expect that there be a TResponse provided using the .WithResponse(TResponse) method. The same success/failure mechanism used in the RequestMessage<TRequest> class is also available on this class.

Considerations

If you have a rather predictable sequential workflow and you require something faster execution then you may wish to consider the Shuttle.Core.Pipelines package. A performance testing application for your use-case would be able to indicate the more suitable option.