{"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.AsyncEnumerator.MoveNextAsync()\n   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable\u00601 source, CancellationToken cancellationToken)\n   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable\u00601 source, CancellationToken cancellationToken)\n   at Bulev.Library.Products.BookmarksRepository.AddAsync(Sessions session, Int64 productid) in E:\\_disk c\\_work\\_projects\\ZigZagDom\\Bulev.Library.Products\\Bulev.Library.Products\\Repositories\\BookmarksRepository.cs:line 34\n   at Bulev.Library.Products.BookmarksIM.Add(BaseController controller) in E:\\_disk c\\_work\\_projects\\ZigZagDom\\Bulev.Library.Products\\Bulev.Library.Products\\Models\\Bookmarks.cs:line 51"}