public GroupTripOrder orderGroupTrip(GroupTrip groupTrip, PaymentType paymentType, Address orderAddress, User user)
        {
            if (!this.users.Contains(user))
            {
                return(null);
            }

            if (groupTrip == null || orderAddress == null || user == null || !this.canOrderGroupTrip(groupTrip))
            {
                return(null);
            }

            if (groupTrip.saveInDB() == null)
            {
                return(null);
            }

            GroupTripOrder groupTripOrder = new GroupTripOrder(paymentType, DateTime.Now, user, orderAddress, ++numOrders, groupTrip);

            DAL.Order value = groupTripOrder.saveInDB();

            if (value == null)
            {
                return(null);
            }

            // value.boatToursManagerId = 1;
            entity.numOrders = this.numOrders;
            db.SaveChanges();

            this.orders.Add(groupTripOrder.orderNumber, groupTripOrder);
            return(groupTripOrder);
        }