The Command Pattern

In recent years, I have rarely completed a web project without deploying this pattern. Originally conceived in the context of graphical user interface design, command objects make for good enterprise application design, encouraging a separation between the controller (request and dispatch handling) and domain model (application logic) tiers. Put more simply, the Command pattern makes for systems that are well organized and easy to extend.

The Problem

All systems must make decisions about what to do in response to a user's request. In PHP, that decision-making process is often handled by a spread of point-of-contact pages. In selecting a page (feedback.php), the user clearly signals the functionality and interface she requires. Increasingly, PHP developers are opting for a single-point-of-contact approach (as I will discuss in the next chapter). In either case, however, the receiver of a request must delegate to a tier more concerned with application logic. This delegation is particularly important where the user can make requests to different pages. Without it, duplication inevitably creeps into the project.