public override IAnswer execute()
        {
            List<Database.Airport> airports = new List<Database.Airport>();
            if (this.City != null) {
                airports = executeOnCity();
            } else if (this.Country != null) {
                airports = executeOnCountry();
            }

            Database.AirlineRequest alr = new Database.AirlineRequest();
            List<Airport> resultAirports = new List<Airport>();
            foreach(Database.Airport a in airports){
                Database.CityRequest cir = new Database.CityRequest();
                Database.CountryRequest cor = new Database.CountryRequest();
                Database.City ci = cir.fetchFromID(a.city)[0];
                Database.Country co = cor.fetchFromID(a.country)[0];

                Country country = new Country(co.name);

                List<Airline> airlines = new List<Airline>();
                foreach(int airline in a.company){
                    Database.Airline al = alr.fetchFromID(airline)[0];
                    airlines.Add(new Airline(Name: al.name, Code: al.code));
                }
                resultAirports.Add(new Airport(Name: a.name, Code: a.code, City: new City(ci.name, country), Airlines: airlines));
            }

            return new AnswerGetAirports(resultAirports);
        }
        public override IAnswer execute()
        {
            Database.CountryRequest cor = new Database.CountryRequest ();
            Database.CityRequest cir = new Database.CityRequest ();

            if (this.Airport.City == null) {
                return new AnswerAdd("The city of the airport isn't set.");
            }

            List<Database.Country> countries = cor.fetchCountryFromName (this.Airport.City.Country.Name);
            if (countries.Count != 1) {
                return new AnswerAdd ("No (unique) country found with name " + this.Airport.City.Country.Name);
            }
            int countryID = countries [0].ID;

            List<Database.City> cities = cir.fetchFromNameAndCountry(this.Airport.City.Name, this.Airport.City.Country.Name);
            if (cities.Count != 1) {
                return new AnswerAdd("No (unique) city found with name " + this.Airport.City.Name + " in country " + this.Airport.City.Country.Name);
            }
            int cityID = cities[0].ID;

            AnswerAdd aa = new AnswerAdd ();
            Database.Airport airport = new Database.Airport (name: this.Airport.Name, code: this.Airport.Code, country: countryID, city: cityID);

            try {
                airport.insert();
            } catch (Database.InvalidObjectException e){
                aa = new AnswerAdd(e.Message);
            } catch (Exception e) {
                aa = new AnswerAdd(e.ToString());
            }

            return aa;
        }
        public override IAnswer execute()
        {
            Database.CityRequest cr = new Database.CityRequest();
            List<Database.City> cities = cr.fetchCityFromCountry(new Database.Country(this.Country.Name));
            List<City> resultCities = new List<City>();
            foreach(Database.City c in cities){
                resultCities.Add(new City(Name: c.name, Country: this.Country));
            }

            return new AnswerGetCities(resultCities);
        }
        private List<Flight> adapt(List<Database.Flight> dfs)
        {
            Database.FlightTemplateRequest ftr = new Database.FlightTemplateRequest();
            Database.AirlineRequest alr = new Database.AirlineRequest();
            Database.AirplaneRequest apr = new Database.AirplaneRequest();
            Database.LocationRequest lr = new Database.LocationRequest();
            Database.SeatRequest sr = new Database.SeatRequest();
            Database.ClassRequest cr = new Database.ClassRequest();
            Database.CountryRequest cor = new Database.CountryRequest();
            Database.CityRequest cir = new Database.CityRequest();
            Database.AirportRequest ar = new Database.AirportRequest();

            List<Flight> fs = new List<Flight>();
            foreach(Database.Flight f in dfs){
                Database.FlightTemplate ft = ftr.fetchFromID(f.template)[0];
                Database.Airline airline_ = alr.fetchFromID(ft.airline)[0];

                Airline airline = new Airline(Name: airline_.name, Code: airline_.code);
                FlightTemplate template = new FlightTemplate(ft.digits, airline);

                Database.Location l = lr.fetchFromID(f.location)[0];
                Database.Airport startAirport_ = ar.fetchFromID(l.start_airport)[0];
                Database.Airport destinationAirport_ = ar.fetchFromID(l.destination_airport)[0];

                Country startCountry = new Country(cor.fetchFromID(startAirport_.country)[0].name);
                Country destinationCountry = new Country(cor.fetchFromID(destinationAirport_.country)[0].name);

                City startCity = new City(cir.fetchFromID(startAirport_.city)[0].name, startCountry);
                City destinationCity = new City(cir.fetchFromID(destinationAirport_.city)[0].name, destinationCountry);

                Airport startAirport = new Airport(startAirport_.name, startAirport_.code, startCity);
                Airport destinationAirport = new Airport(destinationAirport_.name, destinationAirport_.code, destinationCity);

                Database.Airplane airplane_ = apr.fetchFromID(f.airplane)[0];

                List<Seat> seats = new List<Seat>();
                foreach(int s in airplane_.seat){
                    Database.Seat seat_ = sr.fetchFromID(s)[0];
                    Database.Class seatClass_ = cr.fetchFromID(seat_.class_)[0];
                    SeatClass seatClass = new SeatClass(seatClass_.name);
                    seats.Add(new Seat(seatClass, seat_.number));
                }

                Airplane airplane = new Airplane(airplane_.type, seats, airplane_.code);

                fs.Add(new Flight(template, f.start, f.end, startAirport, destinationAirport, airplane));
            }

            return fs;
        }
        private List<Database.Flight> executeOnCity()
        {
            Database.CityRequest cr = new Database.CityRequest ();

            List<Database.City> cities = cr.fetchFromNameAndCountry (City1.Name, City1.Country.Name);
            if (cities.Count () != 1) {
                throw new Exception ("A (unique) city with name " + City1.Name + " and country " + City1.Country.Name + " couldn't be found");
            }
            Database.City startCity = cities [0];

            cities = cr.fetchFromNameAndCountry (City2.Name, City2.Country.Name);
            if (cities.Count () != 1) {
                throw new Exception("A (unique) city with name " + City2.Name + " and country " + City2.Country.Name + " couldn't be found");
            }
            Database.City endCity = cities [0];

            return doDispatch(startCity, endCity);
        }