IDs to Objects

A few months ago I blogged about Domain Objects vs. Primitive Types. Back then it felt right to me to transform a primitive type, like a Guid that represented an organization ID, to an Organization domain object. Unfortunately at that time I was not educated enough to know that this is a common idiom among many object designers. Apparently it is. Craig Larman writes it nicely in his book (in my case Organization is what Craig references to as a Customer):

Why bother? Having a true Customer object that encapsulates a set of information about the customer, and which can have behaviour , frequently becomes beneficial and flexible as the design grows, even if the designer does not originally perceive a need for a true object and thought instead  that a plain number of ID would be sufficient.

The other important note is when this transformation is taking place - when an ID or a Key leaves the UI layer and gets to the Domain Layer.