Find SignalR client by ID in its context

Question

So I want to send a message to a specific client via SignalR. That client is not Clients.Caller - currently I can only identify it by let's call it "ID", a property in the context: this.Context.Items["ID"]

So to find a client by its ID, how do I...access all clients or contexts? Or should I save this ID in a different way? This is not the connection ID, it is an ID that maps to something in the database.

Basically I'd like to go Clients.Single(c => c.Items["ID"] == specificId).SendMessage(msg);

Answer 1

In the OnConnectedAsync method in your hub, you can group a user by their "ID" each time they connect.

E.G:

public async override Task OnConnectedAsync()
{
    var currentUserId = /*get your current users id here*/
    await Groups.AddToGroupAsync(Context.ConnectionId, $"user-{currentUserId}");
    await base.OnConnectedAsync();
}

Then when you need to send that person a message, you can just broadcast it to their 'personal' group. (One person may have multiple connections, so the group approach work perfectly for us).

E.G:

Clients.Group($"user-{userId}").SendAsync("UserSpecificMessage", message);

When users disconnect, SignalR will handle the removing of connections from the groups automatically.

In using this approach, we do not have to unnecessarily broadcast a message to every single client with the intention of only one client filtering out the message based on the id.