How to get delayed response with SignalR (Controller calls Background Service)?-CodePudding

I read documentation and tutorials about SignalR. But I don't understand how to get response in my situation.

.Net5.

Reactjs sends request to Controller.

Controller action:

[HttpGet("compared")]
public async Task<ActionResult> GetComparedText([FromQuery] PrevDraftVersionDto dto) =>
            Ok(await _mediator.Send(new GetComparedTextQuery(dto.InitialDraftId, dto.DraftId, dto.CurrVer, dto.PrevVer)));

GetComparedTextHandler

public class GetComparedTextHandler : IRequestHandler<GetComparedTextQuery, ComparedDraftDto>
    {
        private readonly AppDbContext _appDbContext;
        private readonly TpaChannel _tpaChannel;

        public GetComparedTextHandler(AppDbContext appDbContext, TpaChannel tpaChannel)
        {
            _appDbContext = appDbContext;
            _tpaChannel = tpaChannel;
        }

 public async Task<ComparedDraftDto> Handle(GetComparedTextQuery request, CancellationToken cancellationToken)
{
   var edDraftComparison = ...// get compared text from repository
   if (edDraftComparison == null) {
      Repository doesn't have record yet.

   // 1) Adding to repository request.InitialDraftId, request.DraftId
   .........

  // 2) Create Channel for background Service
   message = "added_to_queue";
                var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                cts.CancelAfter(TimeSpan.FromSeconds(180)); // wait max  seconds
                var versionDto = new VersionDto(request.InitialDraftId, request.DraftId, request.CurrVer, request.PrevVer);
                await _tpaChannel.AddVersionsAsync(versionDto, cts.Token);

} // if (edDraftComparison == null)
else {...}
return ....
}

Handler sends response to Controller and to web client. But after all tpaChannel start Background Service. It updated a record (by InitialDraftId) in repository.

And then I need to get updated record with SignalR.

I read tutorials, that Controller action can load signalR:

hubContext.Clients.User(UserId).SendAsync(
            "receiveUpdatedText",
            new Article<LikeRelatedPayload>
            {
                DraftId = draftId,
                Payload = payload
            }
        );

But it is wrong idea, because, I have to get record from repository after Background Service job.

Where I need to create a singnalR service, that it will send record from Background Service to current user?

Sorry for language, it is difficult for me to explain situation in English.

CodePudding user response：

How about make use of IHubContext in your corresponding background service. I don't know what our background service look like... so I'll just describe some dummy one

public abstract class DummyProcessor : Microsoft.Extensions.Hosting.BackgroundService
{
    IHubContext<MyHub> _myHub;

    protected DummyProcessor(IHubContext<MyHub> myHub)
    {
        ServiceScopeFactory = serviceScopeFactory;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        // some logic...
        await _myHub.Clients.All.SendAsync("As we usually do");
    }
}