Design suggestion for an invoice application

Question

I am trying to make an invoice management system for our company. I am a little bit confused because of design principles. SOLID

Lets say that a class takes care of invoices: InvoiceProcessor

InvoiceProcessor ip=new InvoiceProcessor(DraftHTML);
ip.Customer=theCustomer;
ip.Order=theOrder;
ip.Prepare();

After this, which approach is better? And why?

A)

ip.SaveToFile(fileName);
ip.SendToCustomer();

ip.DBConnection=myActiveConnection;
ip.LoadFromDB(invoiceID);
ip.SaveToDB();

B)

SaveToFile(fileName,ip.GetHTML());
SendEmail(ip.Customer,ip.GetHTML());

ip.InvoiceInfo=LoadFromDB(invoiceID);
SaveToDB(ip.InvoiceInfo);

To me -- it makes more sense for the domain, InvoiceProcessor, to deal with things related to processing an invoice. Therefore, option B makes the most sense. — Ian P, May 28 '14 at 13:26
I see a lot of responsibilities (preparing/creating-an-invoice, loading, saving, sending-email) and only a single class - This breaks SOLID already. — Maarten, May 28 '14 at 13:34

score 4 · Accepted Answer · answered May 28 '14 at 13:33

Imho, both A) and B) break the SRP principle, although B) is less coupled.

I would approach this in another way:

Create a new type which represents an Invoice
Make InvoiceProcessor return an instance of Invoice
For each post processing step create a different type of action.

The code should look like this:

var ip = new InvoiceProcessor
{
    Customer = theCustomer,
    Order = theOrder
};
var invoice = ip.CreateInvoice();
// Post processing
HtmlPrinter.PrintInvoice(invoice, htmlFileName);
DataAccess.SaveInvoice(invoice);
MailService.SendInvoiceToCustomer(invoice, theCustomer.Email);

score 0 · Answer 2 · answered May 28 '14 at 13:26

B option is better because you can use your methods in various ways. If you choose your first suggestion, in the future if you want to write a code let's say for your dispatches, then you have to write same code again for dispatch part . That will cause a bad pattern in your code. You should avoid repetitive code as possible as you can.

Design suggestion for an invoice application

2 Answers2