public int SaveBooking(Booking b)
        {
            try
            {
                int j = -1;
                LINQDBDataContext dc = new LINQDBDataContext();

                IQueryable<int> d = from r in dc.Bookings
                                    orderby r.booking_id ascending
                                    select r.booking_id;
                foreach (int i in d)
                {
                    j = i;
                }
                
                b.booking_id = j + 1;

                dc.Bookings.InsertOnSubmit(b);
                dc.SubmitChanges();
            }
            catch (Exception)
            {
                return -1;
            }
            return b.booking_id;
        }
 public int SaveCustomer(Customer c)
 {
     try
     {
         LINQDBDataContext dc = new LINQDBDataContext();
         dc.Customers.InsertOnSubmit(c);
         dc.SubmitChanges();                        
     }
     catch (Exception)
     {
         return -1;
     }
     return 0;
 }
        public ReviewModel GetReview(int vehicle_id)
        {
            LINQDBDataContext dc = new LINQDBDataContext();
            List<ReviewModel> rm = (from v in dc.Vehicles
                                    join mdl in dc.Models on v.model_code equals mdl.model_code
                                    join vc in dc.VehicleCategories on v.vehicle_category_code equals vc.vehicle_category_code
                                    join mf in dc.Manufacturers on v.manufacturer_code equals mf.manufacturer_code
                                    where v.vehicle_id == vehicle_id
                                    select new ReviewModel
                                    {
                                        registration_number = v.registration_number,
                                        manufacturer_name = mf.manufacturer_name,
                                        model_code = v.model_code,
                                        body_style = mdl.body_style,
                                        automatic = mdl.automatic,
                                        passenger_capacity = mdl.passenger_capacity,
                                        vehicle_category_description = vc.vehicle_category_description,
                                        manufacturing_date = v.manufacturing_date,
                                        availability = v.availability,
                                        daily_rental_rate = v.daily_hire_rate
                                    }).ToList();

            return rm[0];
        }