Interface programming

Question

Background

A developer on my team has implemented an application which I was reviewing. He has used interfaces everywhere. The app has typical service layer, data layer and POCO objects passed from website down to DB.

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Assumption

IOC used (through Unity) to inject a runtime concrete Service and Data class. All POCOs have nothing but get and set methods on public properties.

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Question

I understand why an interface is used at the Service and Data layer but why would you use interfaces on all POCO objects? Is this overkill?

Answer 1

Do the POCO interfaces serve a purpose? If yes, they may not be overkill. However, if they are not used, they violate the YAGNI principle.

However, on a more general note, I'm beginning to think that properties on interfaces are design smells, as they violate the Law of Demeter.

I recently posted some thoughts on better abstractions.

Answer 2

It looks like your POCOs are used simply as Data Transfer Objects. If that's the case, they're just carrying information, with no behavior. Creating interfaces for them is overkill.