WorkingEntitySetStateApproach.cs

var invoiceEntity = new Entity(Invoice.EntityLogicalName) { Id = invoiceRef.Id };
// do not attempt to set the statecode - if you do this code will fire workflows twice
// invoiceEntity["statecode"] = new OptionSetValue((int)InvoiceState.Active);
invoiceEntity["statuscode"] = new OptionSetValue((int)invoice_statuscode.ReadyToIssue);
tracingService.Trace("Update invoice status to Ready To Issue, Id:{0}", invoiceEntity.Id);
service.Update(invoiceEntity);