ASP.NET MVC: Coordinators and Worker Services

Responsibility-Driven Design defines two concepts that work very well in ASP.NET MVC: controller and coordinator. Needless to say, an RDD controller has little to do with an ASP.NET MVC controller. In RDD, a controller orchestrates the behavior of other objects, and decides what other objects should do. In one word, it suggests a chatty communication model. An RDD coordinator, instead, adds one more layer around controllers. A coordinator, in fact, solicited by events delegates work to other objects. In doing so, it applies a chunky communication model.

Great. What about ASP.NET MVC controllers? Should they be controllers or coordinators? Should they be chatty or chunky?

An ASP.NET MVC controller that chats with the site’s backend is not really better than a so much snubbed code-behind class. An ASP.NET MVC controller that behaves like an RDD coordinator groups all of the steps that form the implementation of the action within a single worker object. You place a single call to the worker object and use its output to feed the view-model object.

You break down the complexity of the task requested into steps and code them into a worker service that is 1:1 with the controller. The controller method is then as simple as

public ActionResult Index()
{
    var model = _workerService.GetIndexViewModel();
    return View(model);
}

You have no need to test controllers any more and, better, pass any information down to the worker service which is completely isolated from the HTTP context.

Reworked quote from: Programming ASP.NET MVC4 (Microsoft Press, 2013)