Single-Project Areas in ASP.NET MVC 2

The ASP.NET MVC framework brought a lot of benefits to the Microsoft web developer, such as easier automated testing and better separation of concerns, but it did come with its share of pain points.  One of those pain points was the difficulty of organizing the files in your web project.  By default, all folders that contained views, which were named after the controllers in your application, had to be directly under the “Views” folder that was provided by the framework.  For large applications, the number of folders underneath “Views” could get quite unwieldy.

To help alleviate this, in the first preview of version 2 of the MVC framework, the concept of “Areas” was introduced to allow an additional hierarchical level to controller and view organization.  It was implemented in Preview 1 using separate web projects for each area, each with its own “Controllers” and “Views” folder.

This was a definite improvement, but there was some pretty quick feedback from the community about the implementation.  Having a separate project for each area means that large solutions would end up with quite a few projects, which can dramatically impact compilation time.  I can speak from experience; the main solution I work on had over 80 projects in it when I first joined my current team.  Build time  was usually about 10 minutes, and that was just compilation, no tests or other things going on in the build.  When we reduced it to three projects, build time went down to about 10 seconds.  Needless to say, as our team starts thinking about doing some MVC work, we don’t want to go back to that place.

Thankfully, in preview 2, the MVC team provided the ability to create all your areas within a single web project.  This provides all the organizational benefits without the impact to compilation time.  To add areas to your MVC web project, follow these steps:

  1. Add a folder named “Areas” to your web project.
  2. Add a folder underneath the Areas folder with the name of the area you want to create, “Accounting” for example.
  3. Add a folder called “Controllers” under the Accounting folder.  Now, when you right-click on this folder, you’ll get the “Add Controller” context menu option.
  4. Add a folder called “Views” under the Accounting folder.  This will work just like the Views folder that gets created as part of the MVC project template.  You’ll have one folder inside the Views folder for each controller in your area.
  5. Add a new class  file to the Accounting folder named “Routes.cs”.  This class will need to inherit from AreaRegistration and override the AreaName property.  It should end up looking something like this:
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Web.Mvc;
    
    namespace MyProject.Areas.Accounting
    {
        public class Routes : AreaRegistration
        {
            public override string AreaName
            {
                get { return "accounting"; }
            }
    
            public override void RegisterArea(AreaRegistrationContext context)
            {
                context.MapRoute(
                    "accounting_default",
                    "accounting/{controller}/{action}/{id}",
                    new { controller = "Invoices", action = "ShowUnpaid", id = "" }
                );
            }
        }
    }
  6. You’ll also need to add a line to your Global.asax.cs file.  Simply call “AreaRegistration.RegisterAllAreas();” just before the first call to routes.MapRoute().

That’s it!  Well, almost.  Since you can have more than one area with the same controller name, when you create an ActionLink or something similar, you have to specify which area you intend to link to.  For instance, if you wanted to link to the ShowUnpaid action of the Invoices controller in the Accounting area from some other area, you’d do it like so:

    <%= Html.ActionLink("Unpaid Invoices", "ShowUnpaid", "Invoices", new {area = "accounting"}, null) %>

Note that if you’re linking to a controller from a view within the same area, you don’t have to specify it in the ActionLink call.

I think this is a great feature, and should allow us to maintain the current level of logical partitioning within our application.  Thanks to the MVC team for putting this in!

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