Sending MediatR INotifications to the client over SignalR

For every INotification you want to send to the client over SignalR, you have to create an INotificationHandler for that specific notification, which then calls the hubcontext to send a specific INotificationMessage (another object alltogether) to the connected clients.

In my app I’m building, I have already quite some notifications like that, and was thinking we could make this probably generic in a way you don’t have to create separate INotificationHandlers and INotificationMessages for all the INotifications you want to be sent to the client as well.

In my research around this, I found this article which is looking very close to what we need: https://remibou.github.io/Realtime-update-with-Blazor-WASM-SignalR-and-MediatR/ There’s an issue there though pointed out in the comments… and another pointer to an interesting library in this regard: https://github.com/KuraiAndras/MediatR.Courier

I think combining those 2 should be able to give a a nice implementation of something like this…

[fretje]

Oh, an about the INotificationMessage: I’ve updated that interface to just be a marker interface. There were 2 properties in there:

One was string MessageType, which in every implementation returned the value nameof(SpecificNotificationMessage). Which was then only used in INotificationService, to us as methodName parameter in the HubContext.SendAsync calls. There, I simply replaced notification.MessageType with notification.GetType().Name in every call to hubContext.SendAsync, which does exactly the same thing (without having to implement a MessageType string on every INotificationMessage…

The other one was just string Message which wasn’t actually needed in every INotificationMessage so no need to be on the Interface. One can easily implement it if it’s actually needed for a specific INotificationMessage.

Maybe this should be in another issue… but I can create a separate PR for this if you want… just let me know!

[jay-cascade]

Like this:

public class MyEventNotification : IEvent, INotificationMessage
{
}

So something like this should work?

public class HomeCreateNotificationEvent : IEvent, INotificationMessage {
  public string Name { get; set; } = default!;
  public string? Description { get; set; }
  public string Phone { get; set; } = default!;
  public string Colour { get; set; } = default!;
  public string Adr1 { get; set; } = default!;
  public string? Adr2 { get; set; }
  public string? Adr3 { get; set; } = default!;
  public string Town { get; set; } = default!;
  public string? County { get; set; }
  public string PostCode { get; set; } = default!;
}

public class CreateHouseRequestHandler : IRequestHandler<CreateHomeRequest, Guid>
{
    // Add Domain Events automatically by using IRepositoryWithEvents
    private readonly IRepositoryWithEvents<Home> _repository;
    private readonly IEventPublisher _publisher;
    public CreateHouseRequestHandler(
      IRepositoryWithEvents<Home> repository,
      IEventPublisher publisher
    ) => (_repository, _publisher) = (repository, publisher);

    public async Task<Guid> Handle(CreateHomeRequest request, CancellationToken cancellationToken)
    {
        var home = new Home(
          request.Name,
          request.Description,
          request.Phone,
          request.Colour,
          request.Adr1,
          request.Adr2,
          request.Adr3,
          request.Town,
          request.County,
          request.PostCode);

        await _repository.AddAsync(home, cancellationToken);

        await _publisher.PublishAsync(
          new HomeCreateNotificationEvent {
          Name = home.Name,
          Description = home.Description,
          Phone = home.Phone,
          Colour = home.Colour,
          Adr1 = home.Adr1,
          Adr2 = home.Adr2,
          Adr3 = home.Adr3,
          Town = home.Town,
          County = home.County,
          PostCode = home.PostCode
        });

        return home.Id;

    }