Edit model object doesn't bind to view as expected

Question

I'm using ASP.NET MVC (1.0), Spark View Engine (1.0) and SubSonic (3.0.0.3).

I'm having some trouble getting an "Edit" view to work correctly. So, in my controller, I have the following controller action that displays the edit form view:

[AcceptVerbs(HttpVerbs.Get)]
public virtual ActionResult Edit(string name)
{
    var plot = Plot.SingleOrDefault(p => p.UserID == LoggedInUser.ID && p.UrlFriendlyName == name);
    // ViewData["plot"] = plot;
    return View(plot);
}

The form on that view posts back to the following controller action:

[AcceptVerbs(HttpVerbs.Post)]
public virtual ActionResult Edit(Plot plot)
{
    var validator = new PlotValidator();
    try
    {
        var results = validator.Validate(plot);
        if (!results.IsValid)
        {
            ...
        }
    }
}

The problem that I'm having, is that the first controller action doesn't actually populate the form with the values from the Plot object submitted to it. The only way I can get it to populate the form is by adding the Plot to ViewData:

ViewData["plot"] = plot;

That populates the edit form, but when I edit the values, and submit it back to the second controller action listed above, it just sends back, basically a new plot with the new values, not the plot sent to the edit form with updated values.

I'm sure I'm probably just missing something simple, but I can't seem to figure out what it is. All of the fields on my form have IDs that are prefixed with "plot."

Anyone know/see what I'm doing wrong? Thanks.

Answer 1

I don't know how it's done in the Spark view engine, but in the out-of-the-box view engine that comes with ASP.NET MVC, this is done by inheriting a strongly-typed view model object in the page using a page directive, rather than using the dictionary that comes with the plain-vanilla ViewPage.

So, instead of the first line of code in the view looking like this:

<%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" 
 Inherits="System.Web.Mvc.ViewPage" %>

It will look more like this:

<%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" 
     Inherits="System.Web.Mvc.ViewPage<HomePageViewModel>" %>

Your current controller code is expecting a strongly-typed object, but it is getting back a ViewData Dictionary instead. So no binding is occurring.

Consider reviewing the following podcast:

Exploring how to use ViewData (Strongly typed and weak typed) with Spark http://www.dimecasts.net/Casts/CastDetails/117

Answer 2

Hey Robert - I don't know how Spark handles it's data, but I can tell you that the second part is pretty simple to fix.

First - you have to remember MVC won't reach into the DB for you. In your case your criteria for pulling out a record seems to involve two criteria - so you'll have to pull that again if you want to make sure the data is set properly. So on POST change your signature to this:

[AcceptVerbs(HttpVerbs.Post)]
public virtual ActionResult Edit(string id, FormCollection form)
{
//assuming you have some kind of PK
var plot = Plot.SingleOrDefault(p => p.ID == id);    
UpdateModel(plot, form.ToValueProvider());
var validator = new PlotValidator();
    try
    {
        var results = validator.Validate(plot);
        if (!results.IsValid)
        {
            ...
        }
    }
}

This is freehanded - but it's how you have to do it with L2S anyway...