public ObservableCollection<House> getAllRelatedHouse() { if (!isValid(new List<string>() { "prID", "vName", "vBoundary", "vInUse" })) return null; ObservableCollection<House> houseList = new ObservableCollection<House>(); string sqlCommand = String.Format("select hID from House where vID={0}", vID); Sql sql = new Sql(); SqlDataReader reader = sql.selectHouseIDByVID(sqlCommand); if (reader.HasRows) { while (reader.Read()) { int hID = Int32.Parse(reader[0].ToString()); House house = new House(); house.id = hID; house.select(); houseList.Add(house); } sql.closeConnection(); return houseList; } else { sql.closeConnection(); return null; } }