{"Error":"A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.","StackTrace":"   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()\n   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable\u00601.Enumerator.MoveNext()\n   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable\u00601 source)\n   at Bulev.Library.Orders.CartsRepository.AddAsync(Sessions session, Int64 productid, Int32 count) in E:\\_disk c\\_work\\_projects\\ZigZagDom\\Bulev.Library.Orders\\Bulev.Library.Orders\\Repositories\\CartsRepository.cs:line 69\n   at Bulev.Library.Orders.CartsIM.AddJsonAsync(BaseController controller) in E:\\_disk c\\_work\\_projects\\ZigZagDom\\Bulev.Library.Orders\\Bulev.Library.Orders\\Models\\Carts.cs:line 84"}