title: Adding user to group in SignalR
body: <p>When adding a new user to a group in my <code>SignalR Hub</code>, how do I check to see if the user has already been added to that particular group? Do I even need to worry about this?</p>
  
  <p>In my <code>SignalR</code> based chat app, there are multiple chat rooms and a user can participate in multiple rooms simultaneously. Every time the user clicks a chat room, I set it as the active room and this invokes a call to my <code>SignalR Hub</code> to make sure the user is in the group -- using the following line:</p>
  
  <pre><code>await Groups.AddAsync(Context.ConnectionId, roomId);
  </code></pre>
  
  <p>I just want to make sure that if my code tries to add a connectionId to a group more than once, I won't get any errors which is why I'm trying to find out if I need to worry about this scenario. If so, how I can check current connectionId's in a particular group.</p>
  
  <p>BTW, I'm coding this in the latest version of <code>SignalR</code> which is a part of ASP.NET Core 2.1 Preview-1.</p>