what is the user in `Clients.User(user)` in signalr?

Question

Clients.User(user).SendAsync()

what is the user? user id or user name?

Answer 1

Hi @mc ,

Clients.User(user).SendAsync() what is the user? user id or user name?

The user should be the user id, check the definition:

You can refer the following sample, use Asp.net Core Identity to manage user and do the login action.

Code in the Chat hub:

MyChatHub.cs:

namespace SignalRApp.Hubs  
{  
    [Authorize]  
    public class MyChatHub : Hub  
    {  
        //define a dictionary to store the userid.  
        private static Dictionary<string, List<string>> NtoIdMappingTable = new Dictionary<string, List<string>>();  
           
        public override async Task OnConnectedAsync()  
        {  
            var username = Context.User.Identity.Name;  
            var userId = Context.UserIdentifier;  
            List<string> userIds;  
  
            //store the userid to the list.  
            if (!NtoIdMappingTable.TryGetValue(username, out userIds))  
            {  
                userIds = new List<string>();  
                userIds.Add(userId);  
  
                NtoIdMappingTable.Add(username, userIds);  
            }  
            else  
            {  
                userIds.Add(userId);  
            }  
  
            await base.OnConnectedAsync();   
        }  
        public async Task SendMessageToAll(string user, string message)  
        {  
  
            await Clients.All.SendAsync("ReceiveMessage", user, message);  
        }  
  
  
        public async Task SendMessageToReceiver(string sender, string receiver, string message)  
        {  
  
            var userId = NtoIdMappingTable.GetValueOrDefault(receiver);  
  
            if (userId.Count > 0)  
            {  
                await Clients.User(userId.FirstOrDefault()).SendAsync("ReceiveMessage", sender, message);  
            }  
            else  
            {  
                //the userid is null.  
            }  
  
        }  
  
        public override async Task OnDisconnectedAsync(Exception exception)  
        {  
            var username = Context.User.Identity.Name;  
            var userId = Context.UserIdentifier;  
            List<string> userIds;  
  
            //remove userid from the List  
            if (NtoIdMappingTable.TryGetValue(username, out userIds))  
            {  
                userIds.Remove(userId);  
            }    
            await base.OnDisconnectedAsync(exception);  
        }  
    }  
}  

Index.cshtml:

    <div class="container">  
        <div class="row">&nbsp;</div>  
        <div class="row">  
            <div class="col-2">Sender</div>  
            <div class="col-4"><input type="text" id="senderInput" value="@User.Identity.Name" /></div>  
        </div>  
        <div class="row">  
            <div class="col-2">Receiver</div>  
            <div class="col-4"><input type="text" id="receiverInput" /></div>  
        </div>  
        <div class="row">  
            <div class="col-2">Message</div>  
            <div class="col-4"><input type="text" id="messageInput" /></div>  
        </div>  
        <div class="row">&nbsp;</div>  
        <div class="row">  
            <div class="col-6">  
                <input type="button" id="sendButton" value="Send Message" />  
            </div>  
        </div>  
    </div>  

chat.js:

document.getElementById("sendButton").addEventListener("click", function (event) {  
  
    var user = document.getElementById("senderInput").value;  
    var message = document.getElementById("messageInput").value;  
    var receiver = document.getElementById("receiverInput").value;  
    if (receiver.length > 0) {  
        //if the receiver is not empty, send private message to the receiver.  
        connection.invoke("SendMessageToReceiver", user, receiver, message).catch(function (err) {  
            return console.error(err.toString());  
        });  
    }  
    else {   
        //send message to all user.  
        connection.invoke("SendMessageToAll", user, message).catch(function (err) {  
            return console.error(err.toString());  
        });  
    }  
  
    event.preventDefault();  
});  

The result as below:

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Best regards,
Dillion

Answer 2

See docs

https://learn.microsoft.com/en-us/aspnet/core/signalr/groups?view=aspnetcore-5.0