How should I pass data between classes and application layers?

Question

For example, if I am creating a 3 layer application (data / business / UI) and the data layer is grabbing single or multiple records. Do I convert everything from data layer in

Answer 1

There are a lot of great answers here, I would just add that before you spend a lot of time creating translation layers and factories it's important to understand the purpose and future of your application.

Somewhere, whether it's a config mapping file, a factory, or directly in your data/business/ui layer some object/file/class/etc is going to have to have knowledge of what transpires between each layer. If swapping out layers is realistic, then creating the translation layers is useful. Other times, it just makes sense to have some layer (I usually make it in business) know about all Interfaces (or at least enough to broker between data and ui).

Again, this isn't to say all of that stuff is bad, just that it's possible YAGNI. Some DI and ORM frameworks make this stuff so easy that it's stupid not to do it. If you're using one, then it probably makes sense to get it for all it's worth.