How do you handle free-text associations with DDD

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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