how to save SignalR Chat to database

For this issue, I think you should save the user id and the connection id to your database as well as save the messages that are sent in that chat.

Just check below code.

public override System.Threading.Tasks.Task OnConnected()
    {
          // Get UserID. Assumed the user is logged before connecting to chat and userid is saved in session.
          string UserID = (string)HttpContext.Current.Session["userid"];

          // Get ChatHistory and call the client function. See below
          this.GetHistory(UserID); 

          // Get ConnID
          string ConnID =  Context.ConnectionId; 

          // Save them in DB. You got to create a DB class to handle this. (Optional)
          DB.UpdateConnID(UserID, ConnID); 
    }

    private void GetHistory(UserID)
    {
          // Get Chat History from DB. You got to create a DB class to handle this.
          string History = DB.GetChatHistory(UserID); 

          // Send Chat History to Client. You got to create chatHistory handler in Client side.
          Clients.Caller.chatHistory(History );           
    }

     // This method is to be called by Client 
    public void Chat(string Message)
    {
          // Get UserID. Assumed the user is logged before connecting to chat and userid is saved in session.
         string UserID = (string)HttpContext.Current.Session["userid"]; 

         // Save Chat in DB. You got to create a DB class to handle this
         DB.SaveChat(UserID, Message); 

         // Send Chat Message to All connected Clients. You got to create chatMessage handler in Client side.
         Clients.All.chatMessage(Message);  
    }

For more information, please follow below.

https://github.com/SignalR/SignalR/issues/1214

Hope that helps, thanks.