thinking out loud: mvc & nhaml

I’ve been playing around with the view engine nhaml and mvc. At the same time, I’m playing around with some architectural ideas in hope to benefit future projects.

I’m not doing any fancy yet, but I thought that it might be interesting to show you a couple of things to see what you think. Bear in mind, this is my sandbox code. I also suspect that I’m reinventing some wheels.

The context here is a page that allows a user to register for an account on the site.

First, the view looks like this:

%h2 Create Account

  = Html.FormField<OpenAccount>(x=>x.AccountName)
  = Html.FormField<OpenAccount>(x=>x.EmailAddress)
  = Html.FormField<OpenAccount>(x=>x.Password)
  %input {type="submit" value="Save"}
  %button {onclick="javascript:history.back()" type="button"} Cancel

OpenAccount is my view model. (I hate how we’ve overloaded these  terms.)

I really like the succinctness of the nhaml, though I’m not ready to commit to it 100%. Spark is very attractive to me as well.

Html.FormField is an extension method I wrote. I’m toying with the idea of having it emit a <lablel /> paired with the <input />. Part of my motivation here is standardizing all of the label/inputs in my forms as well as a few experimental ideas about localization.

It’s rather naive at the moment, but here is the helper:

public static string FormField<T>(this HtmlHelper helper, Expression<Func<T, string>> property)
    where T : class, ICommand
    var model = helper.ViewData.Model as T;
    if (helper.ViewData.Model != null && model == null) throw new InvalidOperationException();

    var expression = (MemberExpression)property.Body;
    var name = expression.Member.Name;

    var value = (model == null)
                    ? null
                    : property.Compile().Invoke(model);

    return helper.TextBox(name, value);

Yeah, I hardcoded to a textbox for the moment. As I said, this is just a sandbox spike.

Finally, the associated controller action looks like this:

public ActionResult Create(OpenAccount form)
    var result = _backend.Execute(form);

    return result.Success
               ? (ActionResult) RedirectToAction("WhateverIsNext")
               : View(result);

I’m treating the incoming form as a command. The _backend is responsible for processing the command. The command is just information necessary to execute the command, not the logic to execute it. The result I’m getting back is actually an instance of the same command with information attached by the backend (e.g., did the command execute correctly, what were the validation errors). It’s not exactly SRP, however I’m influenced by the simplicity of RoR here.

One more interesting bit. I really don’t like having actions in my controller that do nothing other than render the view. For example:

public ActionResult Create()
    return View();

So instead, I created a base controller that does this:

public class ControllerBase : Controller
    protected override void HandleUnknownAction(string actionName)
        catch (InvalidOperationException e)
            //show the error or something

Posted 10-02-2009 4:48 PM by Christopher Bennage
Filed under: , ,


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