Re: How do you handle free-text associations with DDD

What do you think about a hierarchy of Invoice (the abstract one, derived
by the others), CustomerInvoice and FreeInvoice?
CustomerInvoice would derive Invoice and use a CustomerIdentifier to relate
to the customer and the FreeInvoice would simple use a string.


Giacomo

On Tue, Mar 12, 2013 at 11:16 AM, codewithcoffee
<[email protected]>wrote:

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>
>
>
> Hello All,
>
> I will first present a simple example which I know that I shouldn't talk
> about UI first, but it places the example in a context.
>
> So - imagine two agg. roots: Invoice and Customer. Invoice has an
> association to Customer, but there is also a possibility to define a
> customer for an invoice by simply typing the customer name into the
> "Customer" textbox. I would call this free-text.
>
> There are two possibilities here as I see them:
>
> - have a text property on Invoice in which the customer name is stored
> (I would not go for this at all), and then provide messy code that
> decides what to return when you ask for the Customer.
> - create a new Customer when saving the Invoice, by providing his newly
> typed name since this is the only dependency of the Customer root.
>
> I would always lean for second approach, but take into account that we
> don't want these "free" customers displayed in our "Customers view" for
> example. So, what could you do? Add a property on Customer that would
> distinguish these entries?
>
> I would also presume that since this "feature" is required in the
> domain, we would have requirements like: "User is able to define a Free
> Customer on an Invoice" and an UI requirement like "User should not see
> Free Customers in Customers View".
>
> One option that I see is having inheritence in place here, meaning
> specific entities Customer and FreeCustomer entities, but again I am
> little confused how to model this in DDD way.
> Would FreeCustomer inherit Customer which is agg. root? Would callers of
> interating over all Customers try to cast to FreeCustomer? I generally
> don't like inheritance that much.
>
> This example is completely made up, and I know what there are no
> "concrete" questions here; but I would appreciate any comments about the
> thoughts given here :=)
>
> Best regards, Denis
>
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>