Difference between UserIdentifier, Group name, ConnectionId

[Roy19]

My question relates to SignalR. I'm trying to understand the philosophy behind groups and why do we need them. My question is three fold:

• Can a certain UserIdentifier have multiple ConnectionId(s) under it (suppose I provide a custom implementation of IUserIdProvider or a reconnect event happens in the client)?
• If so then will Clients.User(Context.UserIdentifier).SendAsync() be sending to all users with the same user UserIdentifier?
• If the above is true as well, why even have SignalR groups? Why can't we club multiple ConnectionId(s) within one UserIdentifier and use Clients.User(Context.UserIdentifier).SendAsync() rather than Clients.Group(groupName).SendAsync()?

The purpose of this discussion is to merely understand the philosophy behind UserIdentifier, ConnectionId and Groups rather than ask about a specific scenario.

[engineering87]

I'll try to answer the various points:

Can a certain UserIdentifier have multiple ConnectionId(s)?

Yes, a single UserIdentifier can have multiple ConnectionId(s). This can happen in several scenarios:

• Multiple Devices/Browsers: A user might be connected from different devices or browsers at the same time. Each connection will have its own ConnectionId but will share the same UserIdentifier.

• Reconnects: If a user reconnects due to network issues, the new connection will receive a new ConnectionId. If you are using a custom IUserIdProvider that ties all these connections to the same user, they will share the same UserIdentifier.

Will Clients.User(Context.UserIdentifier).SendAsync() send to all connections with the same UserIdentifier?

Yes, when you call Clients.User(userIdentifier).SendAsync(), SignalR will send the message to all connections associated with that UserIdentifier. This is useful when you want to send a message to a user, regardless of which device or browser they are using, or how many connections they currently have.

Why have SignalR groups if we can use UserIdentifier?

Groups and UserIdentifier serve different purposes, and both are useful in their own contexts:

• UserIdentifier: This is typically used to identify an individual user across multiple connections. When you want to send a message to a specific user across all their connections, Clients.User(userIdentifier).SendAsync() is the right tool.

• Groups: Groups are meant for logically grouping connections that might or might not belong to the same user.