Let AssistantHub update last seen without the possibility of concurre…

…ncy errors

Data/FimRepository.cs

@@ -0,0 +1,18 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace fim_queueing_admin.Data;
+
+/// <summary>
+/// Used for anything that can't be easily done with native EF
+/// </summary>
+/// <param name="dbContext"></param>
+public class FimRepository(FimDbContext dbContext)
+{
+    public async Task<bool> SetCartLastSeen(Guid id, DateTime? lastSeen)
+    {
+        // Note: EF will automatically parameterize this query, id and lastSeen are *not* just substituted in as strings
+        var result = await dbContext.Database.ExecuteSqlAsync(
+            $"UPDATE equipment SET configuration['LastSeen'] = to_jsonb({lastSeen}) WHERE id = {id}");
+        return result > 0;
+    }
+}

Hubs/AssistantHub.cs

@@ -10,32 +10,20 @@
 namespace fim_queueing_admin.Hubs;
 
 [Authorize(AuthTokenScheme.AuthenticationScheme)]
-public class AssistantHub(FimDbContext dbContext, AssistantService assistantService, ILogger<AssistantHub> logger) : Hub
+public class AssistantHub(FimDbContext dbContext, FimRepository repository, AssistantService assistantService, ILogger<AssistantHub> logger) : Hub
 {
     private Guid CartId => Guid.Parse(Context.User?.FindFirst(ClaimTypes.CartId)?.Value ??
                                       throw new ApplicationException("No cart id"));
 
     public override async Task OnConnectedAsync()
     {
-        // await dbContext.Carts.Where(c => c.Id == CartId).ExecuteUpdateAsync(c => c
-        //     .SetProperty(p => p.Configuration!.LastSeen, DateTime.MaxValue));
-        var cart = await dbContext.Carts.FirstOrDefaultAsync(c => c.Id == CartId);
-        if (cart is not null)
-        {
-            cart.Configuration!.LastSeen = DateTime.MaxValue;
-            await dbContext.SaveChangesAsync();
-        }
+        await repository.SetCartLastSeen(CartId, DateTime.MaxValue);
         await SendPendingAlertsToCaller();
     }
 
     public override async Task OnDisconnectedAsync(Exception? exception)
     {
-        var cart = await dbContext.Carts.FirstOrDefaultAsync(c => c.Id == CartId);
-        if (cart is not null)
-        {
-            cart.Configuration!.LastSeen = DateTime.UtcNow;
-            await dbContext.SaveChangesAsync();
-        }
+        await repository.SetCartLastSeen(CartId, DateTime.UtcNow);
     }
 
     /// <summary>

Program.cs

@@ -81,6 +81,7 @@ async Task<string> GetAccessToken()
 
 builder.Services.AddSingleton<IAuthorizationHandler, UserAccessHandler>();
 builder.Services.AddSingleton<DisplayHubManager>();
+builder.Services.AddScoped<FimRepository>();
 builder.Services.AddSignalR();
 
 builder.Services.AddCors(opt => opt.AddDefaultPolicy(pol =>