C#•3w ago

Data Retrieval in a SignalR Hub/Service?

I am used to repo -> service -> controller MVC models, and I do not have much experience with in-memory retrieval beyond using LinQ. Say I have a class which could have multiple queryable fields:

        public string SignalRId { get; set; }
        public int UserId { get; set; }
        public string Nickname { get; set; }
        public string Region { get; set; }
        public string RoomName { get; set; }

        public string SignalRId { get; set; }
        public int UserId { get; set; }
        public string Nickname { get; set; }
        public string Region { get; set; }
        public string RoomName { get; set; }

In a normal appcontextdb access scenario, I would just pull out the values using EFCore LinQ using something like

var user = await _context.Users.FirstOrDefaultAsync(u => u.UserId == UserId)

var user = await _context.Users.FirstOrDefaultAsync(u => u.UserId == UserId)

In my SignalR Hub, I am using an in-memory method and not SQL to store my data since I don't expect users to have long-lasting data (unlikely they will maintain a connection for >5minutes per session). Therefore I inject a ConnectedClientsService and don't have a DB table. - Is using FirstOrDefaultAsync with regular IQueryable is more standard practice in this case (for example, searching for strings matching region, etc)? - Is it standard practice to use 2 concurrent dictionaries with a lock to enable O(1) access?

4 Replies

surwrenOP•3w ago

For reference, this is my code:

public class ConnectedClientsService : IConnectedClientsService {
    private readonly ConcurrentDictionary<int, CMPPlayerDto> _clientsByUserId;
    private readonly ConcurrentDictionary<string, CMPPlayerDto> _clientsByConnectionId;
    private readonly object _lock = new object();
    ...
}

public class ConnectedClientsService : IConnectedClientsService {
    private readonly ConcurrentDictionary<int, CMPPlayerDto> _clientsByUserId;
    private readonly ConcurrentDictionary<string, CMPPlayerDto> _clientsByConnectionId;
    private readonly object _lock = new object();
    ...
}

  public class RoomHub : Hub {
      private readonly IConnectedClientsService _connectedClientsService;

      public RoomHub(IConnectedClientsService connectedClientsService) {
          _connectedClientsService = connectedClientsService;
      }

      public async Task JoinRoom(int userId, string region, string roomName) {
          CMPPlayerDto newPlayer = await CreateCMPPlayer(Context.ConnectionId, userId, region, roomName);
          if (_connectedClientsService.AddClient(newPlayer)) {
              await Groups.AddToGroupAsync(Context.ConnectionId, roomName);   
              await Clients.All.SendAsync("UserJoinedRoom", newPlayer);    
          }
          else {
              ...
          }
      }
      
  }

  public class RoomHub : Hub {
      private readonly IConnectedClientsService _connectedClientsService;

      public RoomHub(IConnectedClientsService connectedClientsService) {
          _connectedClientsService = connectedClientsService;
      }

      public async Task JoinRoom(int userId, string region, string roomName) {
          CMPPlayerDto newPlayer = await CreateCMPPlayer(Context.ConnectionId, userId, region, roomName);
          if (_connectedClientsService.AddClient(newPlayer)) {
              await Groups.AddToGroupAsync(Context.ConnectionId, roomName);   
              await Clients.All.SendAsync("UserJoinedRoom", newPlayer);    
          }
          else {
              ...
          }
      }
      
  }

Imtiaz•3w ago

I believe, for the concurrent dictionary, you don't need a lock object as it is thread safe. Also, FirstOrDefault is fine, but make sure you register IConnectedClientsService as a singleton not scoped or transient.

Unknown User•3w ago

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surwrenOP•3w ago

The lock was to make modifying both dictionaries atomic, is it unnecessary in that case? 😳 I completely did not know this lmao I need to read up

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Data Retrieval in a SignalR Hub/Service?

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