Wednesday, December 31, 2008

Beware Phony Model Objects!

While I am refactoring huge amounts of code out of EJB2 (and trying not to break too much things), I have noticed a bad design pattern that is so noxious I thought I should blog about it.

I call this the Phony Model Objects (PMO) antipattern.

It basically amounts to sharing as first class model objects entities that should never be publicly exposed. These bad citizens may look inocuous at first glance. In fact, they oftentimes carry a deep functional dependency on the technical framework they depend from or are subject to change at a different pace than actual domain objects would do it.

Interestingly I have found that all these PMOs are generated: whether they are EJB2 artifacts (home interfaces, entity beans, value objects, primary keys...) or web service client stubs. This re-enforces the idea that they are by-products and should be treated as such.

So, if you return or accept this kind of PMOs in public methods, do not wait and immediately refactor your code to share only proper domain model objects and keep the phony ones hidden behind the surface of your API.

This will eventually save you a lot of pain and efforts when the technical framework to which your PMOs happen to be coupled to will disappear and you will have to move away from them. Trust me on that one!