How to obtain connection ID of signalR client on the server side?

I need to get the connection ID of a client. I know you can get it from the client side using $.connection.hub.id. What I need is to get in while in a web service I have which updates records in a database, in turn displaying the update on a web page. I am new to signalR and stackoverflow, so any advice would be appreciated. On my client web page I have this:

<script type="text/javascript">
    $(function () {
        // Declare a proxy to reference the hub. 
        var notify = $.connection.notificationHub;
        
        // Create a function that the hub can call to broadcast messages.
        notify.client.broadcastMessage = function (message) {
            var encodedMsg = $('<div />').text(message).html();// Html encode display message.
            $('#notificationMessageDisplay').append(encodedMsg);// Add the message to the page.
        };//end broadcastMessage
                 
        // Start the connection.
        $.connection.hub.start().done(function () {
            $('#btnUpdate').click(function () {
                //call showNotification method on hub
                notify.server.showNotification($.connection.hub.id, "TEST status");
            });
        });

        
    });//End Main function

    
</script>

everything works up until I want to update the page using signalR. The show notification function in my hub is this:

//hub function
public void showNotification(string connectionId, string newStatus){               
    IHubContext context = GlobalHost.ConnectionManager.GetHubContext<notificationHub>();
    string connection = "Your connection ID is : " + connectionId;//display for testing
    string statusUpdate = "The current status of your request is: " + newStatus;//to be displayed
    //for testing, you can display the connectionId in the broadcast message
    context.Clients.Client(connectionId).broadcastMessage(connection + " " + statusUpdate);
}//end show notification

how can I send the connectionid to my web service?

Hopefully I'm not trying to do something impossible. Thanks in advance.

When a client invokes a function on the server side you can retrieve their connection ID via Context.ConnectionId. Now, if you'd like to access that connection Id via a mechanism outside of a hub, you could:

1. Just have the Hub invoke your external method passing in the connection id.
2. Manage a list of connected clients aka like public static ConcurrentDictionary<string, MyUserType>... by adding to the dictionary in OnConnected and removing from it in OnDisconnected. Once you have your list of users you can then query it via your external mechanism.

Ex 1:

public class MyHub : Hub
{
    public void AHubMethod(string message)
    {
        MyExternalSingleton.InvokeAMethod(Context.ConnectionId); // Send the current clients connection id to your external service
    }
}

Ex 2:

public class MyHub : Hub
{
    public static ConcurrentDictionary<string, MyUserType> MyUsers = new ConcurrentDictionary<string, MyUserType>();

    public override Task OnConnected()
    {
        MyUsers.TryAdd(Context.ConnectionId, new MyUserType() { ConnectionId = Context.ConnectionId });
        return base.OnConnected();
    }

    public override Task OnDisconnected(bool stopCalled)
    {
        MyUserType garbage;

        MyUsers.TryRemove(Context.ConnectionId, out garbage);

        return base.OnDisconnected(stopCalled);
    }

    public void PushData(){
        //Values is copy-on-read but Clients.Clients expects IList, hence ToList()
        Clients.Clients(MyUsers.Keys.ToList()).ClientBoundEvent(data);
    }
}

public class MyUserType
{
    public string ConnectionId { get; set; }
    // Can have whatever you want here
}

// Your external procedure then has access to all users via MyHub.MyUsers

Hope this helps!

Taylor's answer works, however, it doesn't take into consideration a situation where a user has multiple web browser tabs opened and therefore has multiple different connection IDs.

To fix that, I created a Concurrent Dictionary where the dictionary key is a user name and the value for each key is a List of current connections for that given user.

public static ConcurrentDictionary<string, List<string>> ConnectedUsers = new ConcurrentDictionary<string, List<string>>();

On Connected - Adding a connection to the global cache dictionary:

public override Task OnConnected()
{
	Trace.TraceInformation("MapHub started. ID: {0}", Context.ConnectionId);
	
	var userName = "testUserName1"; // or get it from Context.User.Identity.Name;

	// Try to get a List of existing user connections from the cache
	List<string> existingUserConnectionIds;
	ConnectedUsers.TryGetValue(userName, out existingUserConnectionIds);

	// happens on the very first connection from the user
	if(existingUserConnectionIds == null)
	{
		existingUserConnectionIds = new List<string>();
	}

	// First add to a List of existing user connections (i.e. multiple web browser tabs)
	existingUserConnectionIds.Add(Context.ConnectionId);

	
	// Add to the global dictionary of connected users
	ConnectedUsers.TryAdd(userName, existingUserConnectionIds);

	return base.OnConnected();
}

On disconnecting (closing the tab) - Removing a connection from the global cache dictionary:

public override Task OnDisconnected(bool stopCalled)
{
	var userName = Context.User.Identity.Name;

	List<string> existingUserConnectionIds;
	ConnectedUsers.TryGetValue(userName, out existingUserConnectionIds);

	// remove the connection id from the List 
	existingUserConnectionIds.Remove(Context.ConnectionId);

	// If there are no connection ids in the List, delete the user from the global cache (ConnectedUsers).
	if(existingUserConnectionIds.Count == 0)
	{
		// if there are no connections for the user,
		// just delete the userName key from the ConnectedUsers concurent dictionary
		List<string> garbage; // to be collected by the Garbage Collector
		ConnectedUsers.TryRemove(userName, out garbage);
	}

	return base.OnDisconnected(stopCalled);
}

I beg to differ on the reconnect. The client remains in the list but the connectid will change. I do an update to the static list on reconnects to resolve this.