public invoice InvoiceCreate(invoice _obj) { objDataContext = new DriveEntities(); if (objDataContext.invoices.Count() > 0) _obj.InvoiceNumber = objDataContext.invoices.Max(x => x.InvoiceNumber) + 1; else _obj.InvoiceNumber = 1; objDataContext.AddToinvoices(_obj); objDataContext.SaveChanges(); //_obj.InvoiceNumber = _obj.id; return _obj; }