Brendan McKenzie

Actions Pattern

Wednesday, 19 November 2014

It's a terrible name, but maybe one day I'll figure a better one. Either way...

Recently we started a new large scale project that is being built in ASP.NET MVC working side-by-side with an Umbraco installation. It got me thinking about the best way to approach the back-end code structure.

Initially we decided on a modular approach, but "modular" is a pretty vague term and wasn't very easy to clearly define. So it soon ended up with some God-classes full of various functions that did a whole lot of things and no clear separation. It was clear to see that this was going to get out of hand very quickly.

The problem brought me back a method I described in a previous post. It basically involves having a base designator that defines a class as one that does something, one thing, it has a specific purpose. The class is given a logical name that simply defines its purpose. These classes only require one thing, an Execute method. That's all that it must have, the parameters and return types can vary as need-be.

In this current project I have called this pattern the Actions Pattern. There is a base interface IAction that has no fields or method descriptors, it's just a basic designator. I then use a DI container (Autofac in this instance) to find all classes that implement IAction and register them.

From there throughout the system I can get an action and execute it.

It's a fairly loose pattern in that the Execute function can be defined as needed, but I feel it allows for the greatest flexibility, but still gives a basic outline on how things should be done.

There are instances where one class may contain multiple Execute methods, but the only viable case for this is when the two (or more) methods do the same thing but with varying parameters.

Now for an example...

1namespace MyApp
2    {
3        public interface IAction { }
4    }
6    namespace MyApp.Authentication
7    {
8        public class AuthenticateUser : IAction
9        {
10            #region Constructor
12            public AuthenticateUser()
13            {
15            }
17            #endregion
19            #region Public Methods
21            public Guid Execute(string userName, string password)
22            {
23                // perform authentication logic here
24            }
26            #endregion
27        }
28    }
30    namespace MyApp.Web.Controllers
31    {
32        public AuthController : Controller
33        {
34            public ActionResult Login()
35            {
36                return View();
37            }
39            public ActionResult Login(string userName, string password)
40            {
41                var userId = GetAction<MyApp.Authentication.AuthenticateUser>().Execute(userName, password);
43                Session["user"] = userId;
45                return Redirect("/");
46            }
48            T GetAction<T>()
49                where T : IAction
50            {
51                return DependencyResolver.Current.GetService<T>();
52            }
53        }
54    }