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;
}