public void AddWare(Ware ware) { List <int> ids = new List <int>(); List <Ware> wares = AllWares().ToList(); foreach (Ware w in wares) { ids.Add(w.Id); } ware.Id = ids.Max() + 1; wares.Add(ware); JsonFileWriter.WriteToJsonWare(wares, JsonFileName); }