public IQueryable <INVOICE> GetByid(int id)
        {
            INVOICERepository rep  = new INVOICERepository(connectionString);
            List <INVOICE>    list = rep.GetDataByid(id);

            return(list.AsQueryable());
        }
        public void Delete(INVOICE invoice)
        {
            INVOICERepository rep = new INVOICERepository(connectionString);

            rep.Remove(invoice);
        }
        public void Put(INVOICE invoice)
        {
            INVOICERepository rep = new INVOICERepository(connectionString);

            rep.Update(invoice);
        }
        public void Post(INVOICE invoice)
        {
            INVOICERepository rep = new INVOICERepository(connectionString);

            rep.Add(invoice);
        }