Posting forms in Sitecore controller renderings – another perspective

Martina Welander, Technical Consulting Engineer at Sitecore, recently blogged about posting forms in Sitecore MVC: Part 1 – View Renderings and Part 2 – Controller Renderings. Especially for controller renderings there are multiple ways of doing it. In this blog post I want to explain another way of doing it. This post is based on the comments on her blog and an SDN forum post.

Recap

In Sitecore MVC the page is rendered by different renderings. This means that on one single page request, there could be multiple controller renderings. In pure ASP.NET MVC, a form is always posted to one certain action, which is marked with the attribute [HttpPost]. In Sitecore this is not possible because the page is rendered through the rendering pipeline and not only through a single action. Martina mentioned several ways of dealing with this:

  • Using @Html.Sitecore().FormHandler() to post to the specific action of the controller rendering. In the action, redirect back to a normal page.
  • Posting the form with Ajax.
  • Manually start the rendering pipeline of Sitecore and work with TempData.
  • Inherit from SitecoreController, calling the base.Index() method and work with TempData.

All this ideas are a bit away from pure ASP.NET MVC. Additionally you may need to deal with TempData and could not use strongly typed view models. Also form validation does not work in every case.

Pure ASP.NET MVC

I like the way how ASP.NET MVC works and I would like to create my Sitecore controllers as near as possible to the standard way. Let’s look into a small example which I would do with pure ASP.NET MVC. I have the following view model:

public class FormModel
{
    [Required]
    public string Name { get; set; }
}

On the GET-request, I want to show a simple form with my name field:

@model Website.Models.FormModel

@using (Html.BeginForm())
{
    @Html.DisplayFor(m => m.Name)
    @Html.TextBoxFor(m => m.Name)
    @Html.ValidationMessageFor(m => m.Name)

    <input type="submit" value="submit"/> 
}

On the POST-request, I want to show a simple success message. If validation fails (remember, my Name-property is required), I want to show the form again. This can be done with the following controller:

public class MyController : Controller
{
    public ActionResult Index()
    {
        return View(new FormModel());
    }

    [HttpPost]
    public ActionResult Index(FormModel model)
    {
        if (!ModelState.IsValid)
        {
            return View(model);
        }

        // do some other stuff, like storing the name in the database

        return View("Success");
    }
}

This code also works with Sitecore MVC, as long as we do not have multiple controller renderings with a form on single page request. If we have, the POST-action of each controller rendering is called instead of the GET-action. But the POST-action should only be called from the controller where the user has posted the form. For all other controller renderings, the GET-action should be called.

Finding the correct POST-action

The initial hint of how to solve this, I’ve found on a blog post from Mike Edwards. I searched for a more generic way of doing this and found, that Sitecore almost implemented this with the FormHandler. I simply add two hidden fields to each of my forms. In my example I would add these:

<input type="hidden" name="fhController" value="MyController"/>
<input type="hidden" name="fhAction" value="Index"/>

This can be manually added into the view, or we could create a custom HtmlHelper function which does this (something similar like Sitecore is doing with @Html.Sitecore().FormHandler()).

This means, that on the POST-request we know which controller/action has forced the post and also which POST-action should be called. With a custom attribute on every POST-action, we can then check if the action is valid or not:

public class ValidateFormHandler : ActionMethodSelectorAttribute
{
    public override bool IsValidForRequest(ControllerContext controllerContext, MethodInfo methodInfo)
    {
        var controller = controllerContext.HttpContext.Request.Form["fhController"];
        var action = controllerContext.HttpContext.Request.Form["fhAction"];

        return !string.IsNullOrWhiteSpace(controller)
                && !string.IsNullOrWhiteSpace(action)
                && controller == controllerContext.Controller.GetType().Name
                && methodInfo.Name == action;
    }
}

The POST-action then gets this additional attribute:

[HttpPost]
[ValidateFormHandler]
public ActionResult Index(FormModel model)
{
    // code
}

Summary

There are many options you have when building forms with Sitecore MVC. None of them are bad or wrong. Several options are more based on Sitecore, the others are more based on pure ASP.NET MVC. It’s up to you what you like more and which one you choose.

What do you think about the different options? Which one do you prefer or do you use in your projects? Are there other options which we have missed?

Kevin Brechbühl

Senior Developer & Architect | C# & ASP.NET | Sitecore Technology MVP

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