ASP.NET MVC Updating a list of objects on one form? (model binding to a list)

Question

Quick question regarding updating a list of items in asp.net mvc.

Basically I have an edit action method that returns a collection of objects (incidentally, the table structure of which looks as follows 'testID, assetID, Result' - a link table).

I basically want this items to be displayed one after another in a form and to be able to edit them. The form should post back and the modelbinder do its magic. But, its not that easy.

I have scoured the net and it seems the majority of the information about this stuff seems to be a little out of date. I've come across this post, which has not been updated in a long time, and this one which seems to suggest that you shouldn't bind to a already existing list for updating, and that there are problems when working with EF or Linq to Sql (which I am).

Is there an easy way to achieve what I want? Has the state of list model binding changed in the release version?

UPDATE - A little closer...

Here's my Edit method:

public ActionResult EditSurveyResults(Guid id)
    {
        var results = surveyRepository.GetSurveyResults(id);
        return PartialView("EditSurveyResults", results);
    }

And my form:

<div id="editSurveyResults">
<h2>
    EditSurveryResults</h2>

<%= Html.ValidationSummary("Edit was unsuccessful. Please correct the errors and try again.") %>
<% using (Html.BeginForm())
   {%>
<fieldset>
    <legend>Results</legend>
    <% int i = 0; foreach (var result in Model)
   { %>

    <input type="hidden" name='results[<%= i %>].TestID' value='<%= result.TestID %>' />
    <input type="hidden" name='results[<%= i %>].AssetID' value='<%= result.AssetID %>' />
    <p>
        <%= result.Task.TaskName%>
    </p>
    <p>
        <label for="Result">
            Result:</label>
        <input type="text" name='results[<%= i %>].Result' value='<%= result.Result %>' />
        <%= Html.ValidationMessage("Result", "*")%>
    </p>

    <% i++; } %>
    <p>
        <input type="submit" value="Save" />
    </p>
</fieldset>
<% } %>

And my Edit POST method:

 [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult EditSurveyResults(Guid id, IList<SurveyTestResult> results)
    {
        var oldValues = surveyRepository.GetSurveyResults(id);

        if (ModelState.IsValid)
        {
            UpdateModel(oldValues);
            surveyRepository.Save();
            return Content("Done");
        }
        else
            return PartialView("EditSurveyResults");
    }

It's not complete of course, but it doesn't update anything in its current state. Am I missing a trick here? results is populated with the the updated entities so I'm not sure why its not updating...

UPDATE 2: So, Im starting to think that the model binder cant do stuff like this. So, I've resorted to doing things in a more hacky way. If anyone can spot a problem with this then please let me know. FYI - this form will be grabbed with AJAX so I dont return a view, rather a simple message. Here's the new code:

IList<SurveyTestResult> oldValues = surveyRepository.GetSurveyResults(id).ToList();
            foreach (var result in SurveyTestResult)
            {
                //SurveyTestResult is the IList that comes down from the form.                    
                SurveyTestResult thisone = oldValues.Single(p => p.AssetID == result.AssetID &&
                    p.TestID == result.TestID);
                //update the old entity with the result from the new one
                thisone.Result = result.Result;
            }

And then I call Save on my repository.

Thanks in advance

Answer 1

One thing i noticed is that your not rendering <input type="hidden" name='results.Index' value='<%= i %>' /> as phil Haacks article mentions is mandatory.

Switching to a different Modelbinder might do the trick too. I use the DataAnnotations model binder and with that i dont have to generate .Index fields when binding to List's.