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

In general, I think it is better to send objects rather than data tables. With objects, each layer knows what it is receiving (which objects with what properties etc.). You get compile time safety with objects, you can't accidentally misspell a property name etc. and it forces an inherent contract between the two tiers.

Joshua also brings up a good point, by using your custom object, you are also decoupling the other tiers from the data tier. You can always populate your custom object from another data source and the other tiers will be none the wiser. With a SQL data table, this will probably not be so easy.

Joel also made a good point. Having your data layer aware of your business objects is not a good idea for the same reason as making your business and UI layers aware of the specifics of your data layer.