using ConsoleApp3.Contracts; namespace ConsoleApp3 { internal class UsedRepository : IUsedRepository { public List Query => File .ReadLines("usedList.csv") .Select(l => l.Split(',')) .Select(p => new String(p[0])) .ToList(); public void insert(string key) { key += Environment.NewLine; File.AppendAllText("usedList.csv", key); } public void Insert(List list) { foreach(var kunde in list) { insert(kunde.BestellungID); } } } }