public String LineCreate(string fkidx, invoiceline line)
        {
            invoice header = db.invoices.Find(Convert.ToInt32(fkidx));

            line.invoice = header;
            db.invoicelines.Add(line);
            db.SaveChanges();
            return("");
        }
        public String LineDelete(string key)
        {
            if (ModelState.IsValid)
            {
                invoiceline data = db.invoicelines.Find(Convert.ToInt32(key));
                db.invoicelines.Remove(data);
                db.SaveChanges();
                return("");
            }

            return("");
        }
        public String LineEdit(string fkidx, invoiceline line)
        {
            if (ModelState.IsValid)
            {
                invoice header = db.invoices.Find(Convert.ToInt32(fkidx));
                line.invoice         = header;
                db.Entry(line).State = EntityState.Modified;
                db.SaveChanges();
                return("");
            }

            return("");
        }