public static Airline GetLetById(int id)
        {
            SqlConnection conn    = new SqlConnection(Program.connectionString);
            Airline       airline = null;

            try
            {
                conn.Open();
                string        query = "select name, airplane, departureAirport, destinationAirport from Airlines where id=" + id;
                SqlCommand    cmd   = new SqlCommand(query, conn);
                SqlDataReader rdr   = cmd.ExecuteReader();

                if (rdr.Read())
                {
                    string   name               = (string)rdr["name"];
                    Airplane airplane           = AirplaneDAO.GetAvionById(id);
                    Airport  departureAirport   = AirportDAO.GetAerodromById(id);
                    Airport  destinationAirport = AirportDAO.GetAerodromById(id);
                    airline = new Airline(id, name, airplane, departureAirport, destinationAirport);
                }
                rdr.Close();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
            finally
            {
                conn.Close();
            }
            return(airline);
        }
        public static List <Airline> GetAll()
        {
            SqlConnection  conn     = new SqlConnection(Program.connectionString);
            List <Airline> airlines = new List <Airline>();

            try
            {
                conn.Open();
                string        query = "select id, name, airplane, departureAirport, destinationAirport from Airlines";
                SqlCommand    cmd   = new SqlCommand(query, conn);
                SqlDataReader rdr   = cmd.ExecuteReader();
                while (rdr.Read())
                {
                    int      id       = (int)rdr["id"];
                    string   imeLeta  = (string)rdr["name"];
                    int      avion    = (int)rdr["airplane"];
                    Airplane airplane = AirplaneDAO.GetAvionById(avion);
                    int      id_aerodrom_poletanje = (int)rdr["departureAirport"];
                    int      id_aerodrom_sletanje  = (int)rdr["destinationAirport"];

                    Airport aerodrom_poletanje = AirportDAO.GetAerodromById(id_aerodrom_poletanje);
                    Airport aerodrom_sletanje  = AirportDAO.GetAerodromById(id_aerodrom_sletanje);

                    Airline airline = new Airline(id, imeLeta, airplane, aerodrom_poletanje, aerodrom_sletanje);
                    airlines.Add(airline);
                }
                rdr.Close();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
            finally
            {
                conn.Close();
            }
            return(airlines);
        }