SignalR - Update specific user (Push notifications)

Question

I'm having troubles to update only one specific user.

I'm working on some asp.net core web application and I want to implement push notification to my project. I'll explain a little more about what am i doing in my application.

I have a page where users can post something (like on facebook). On that post everyone can like/unlike it (like button) or comment it (can delete comments too). And my implementation of signalR on that part is working perfectly with await Clients.All.SendAsync("UpdateComments", userId, postId);.

Now i want to send notification to the user whose post is. I tries to do that on this way await Clients.User(userId).SendAsync("SendNotification", notificationText); but not working. When i debuged it, on this part User(someId) it expect me to send connectionId which i don't have for user which i want to update. I have connectionId only for user who invoked current connection.

My question is: How can i update user with userId from my table or how can i get connectionId based on my userId? OR If i can't on any way to accomplish this, is there a way that i can automatically add user (when he log in to application) in some signalR group connection whithout need for user to activate connection by himself?

I googled a lot, but i didn't found answer. This is link which i followed to implement signalR in my app.

Answer 1

I'm already write small blog post here

You need to write a method to send to specific user id like this

  public async Task Send(string userId)
    {
        var message = $"Send message to you with user id {userId}";
        await Clients.Client(userId).SendAsync("ReceiveMessage", message);
    }

Then listen on event

(function () {
        var connection = new signalR.HubConnectionBuilder().withUrl("/connectionHub").build();

        connection.start().then(function () {
            console.log("connected");

            connection.invoke('getConnectionId')
                .then(function (connectionId) {
                    sessionStorage.setItem('conectionId', connectionId);
                    // Send the connectionId to controller
                }).catch(err => console.error(err.toString()));;


        });

        $("#sendmessage").click(function () {
            var connectionId = sessionStorage.getItem('conectionId');
            connection.invoke("Send", connectionId);
        });

        connection.on("ReceiveMessage", function (message) {
            console.log(message);
        });

    })();