What are Groups in SignalR and how can you use them to manage chat rooms?

Question

ICSM Computer · Answer

In SignalR, Groups are a powerful way to manage
chat rooms, teams, or any logical collection of connected clients.
What Are Groups in SignalR?
A Group is a named collection of connection IDs.A connection (client) can join multiple groups.Groups are dynamic and exist in-memory (per server instance).Useful for features like:
Chat roomsPrivate roomsNotification channels (e.g., user-specific updates)
Key Concepts
Groups are not persisted — clients must rejoin after reconnecting.You manage group membership using Groups.AddToGroupAsync() and 
Groups.RemoveFromGroupAsync().
How to Use Groups
1. Joining a Group (e.g., joining a chat room)
public async Task JoinRoom(string roomName)
{
    await Groups.AddToGroupAsync(Context.ConnectionId, roomName);
    await Clients.Group(roomName).SendAsync("ReceiveSystemMessage", $"{Context.UserIdentifier} joined {roomName}");
}
2. Leaving a Group
public async Task LeaveRoom(string roomName)
{
    await Groups.RemoveFromGroupAsync(Context.ConnectionId, roomName);
    await Clients.Group(roomName).SendAsync("ReceiveSystemMessage", $"{Context.UserIdentifier} left {roomName}");
}
3. Sending a Message to a Group
public async Task SendMessageToRoom(string roomName, string message)
{
    await Clients.Group(roomName).SendAsync("ReceiveMessage", Context.UserIdentifier, message);
}
Client-Side Example (JavaScript)
connection.on("ReceiveMessage", (user, message) =andgt; {
    console.log(`${user}: ${message}`);
});
connection.on("ReceiveSystemMessage", (message) =andgt; {
    console.log(`[System]: ${message}`);
});
// Join a room
connection.invoke("JoinRoom", "room123");
// Send message to room
connection.invoke("SendMessageToRoom", "room123", "Hello everyone!");
Important Tips
Reconnect logic: On client reconnection, the server will not remember previous group memberships. Rejoin groups in
OnConnectedAsync or after reconnecting.Scaling: For distributed apps (multiple servers), use a 
backplane (like Redis) to sync group info across instances.

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What are Groups in SignalR and how can you use them to manage chat rooms?

ICSM Computer

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1 Answers

What Are Groups in SignalR?

Key Concepts

How to Use Groups

1. Joining a Group (e.g., joining a chat room)

2. Leaving a Group

3. Sending a Message to a Group

Client-Side Example (JavaScript)

Important Tips

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