The Selector pattern provides a powerful layer of encapsulation for some critical logic in your application. It can help with enforcing best practices around security and provides a more consistent and reliable basis for code dealing with the SObject data.
Selectors can also take on the responsibility and concern for platform features such as Multi-Currency and Field Sets. Ultimately allowing the caller—be that the Service, Domain, or even Apex Controllers, or Batch Apex—to focus on their responsibilities and concerns, this leads to cleaner code which is easier to maintain and evolve.
With the introduction of the Selector factory, we provide a shortcut to access this layer in the form of the Application.Selector.selectById and Application.Selector.newInstance methods, opening up potential for more dynamic scenarios such as the compliance framework highlighted in the last chapter.
I'd like to close this set of chapters with a simple but expressive diagram that shows how the Service layer...