private string SerializeJson <T>(int idSource, Func <T, bool> predicate = null) where T : class, new() { if (predicate == null) { predicate = (x) => true; } List <T> ds = new List <T>(); if (_dataSource.ContainsKey(idSource)) { ds = _dataSource[idSource].OfType <T>().Where(predicate).ToList(); } var response = new StandardResponse <IEnumerable <T> >() { Data = ds }; return(response.GetJson()); }