asp.net mvc - MVC post a list of complex objects

Question

I have a FeedbackViewModel that contains a list of questions:

public class FeedbackViewModel
{
    public List<QuestionViewModel> Questions { get; set; }
}

This QuestionViewModel is an object that can be inherited by 5 different types of questions

public class QuestionViewModel
{
    public string QuestionText { get; set; }
    public string QuestionType { get; set; }
}

An example of one of the inheriting question types:

public class SingleQuestionViewModel : QuestionViewModel
{
    public string AnswerText { get; set; }
}

In the HttpGet of the Index action in the controller I get the questions from the database and add the correct question type in list of question in the FeedbackViewModel Then I render this model in the view:

@using (Html.BeginForm())
{
    //foreach (var item in Model.Questions)
    for (int i = 0; i < Model.Questions.Count; i++)
    {
        <div class="form-group">
            @Html.DisplayFor(modelItem => Model.Questions[i].QuestionText, new { @class = "control-label col-md-4" })
            <div class="col-md-6">
                @if (Model.Questions[i].QuestionType == "Single")
                {
                    @Html.EditorFor(modelItem => (Model.Questions[i] as OpenDataPortal.ViewModels.SingleQuestionViewModel).AnswerText)
                }
                else if (Model.Questions[i].QuestionType == "Multiple")
                {
                    @Html.TextAreaFor(modelItem => (Model.Questions[i] as OpenDataPortal.ViewModels.SingleQuestionViewModel).AnswerText)
                }
                else if (Model.Questions[i].QuestionType == "SingleSelection")
                {
                    @Html.RadioButtonForSelectList(modelItem => (Model.Questions[i] as OpenDataPortal.ViewModels.SingleSelectionQuestionViewModel).SelectedAnswer,
                                                                (Model.Questions[i] as OpenDataPortal.ViewModels.SingleSelectionQuestionViewModel).SelectionAnswers)
                }
                else if (Model.Questions[i].QuestionType == "MultipleSelection")
                {
                    @Html.CustomCheckBoxList((Model.Questions[i] as OpenDataPortal.ViewModels.MultipleSelectionQuestionViewModel).AvailableAnswers)
                }
                else if (Model.Questions[i].QuestionType == "UrlReferrer")
                {
                    @Html.EditorFor(modelItem => (Model.Questions[i] as OpenDataPortal.ViewModels.SingleQuestionViewModel).AnswerText)
                }
            </div>
        </div>
        <br />
    }

    <br />
    <button type="submit">Submit</button>
}

---

Now, I simply can't get it to post the list of questions in the model. Is it even possible to post a list of different object types?

---

Edit: Following is the list of data within the post that I discovered using Fiddler:

Answer 1

After much research I've found two solutions:

1. One is to write HTML that has hardcoded Id's and Names
2. Two is to convert your ICollection/IEnumerable to an Array or List (i.e IList something with an 'index'), and have an Array object in your BindingModel in your Controller POST Action.

Thanks to Phil Haack's (@haacked) 2008 blog post http://haacked.com/archive/2008/10/23/model-binding-to-a-list.aspx/ Which is still relevant to how the default ModelBinder works today for MVC. (NB: the links in Phil's article to sample porject and extension methods are broken)

HTML snippet that inspired me:

<form method="post" action="/Home/Create">
    <input type="hidden" name="products.Index" value="cold" />
    <input type="text" name="products[cold].Name" value="Beer" />
    <input type="text" name="products[cold].Price" value="7.32" />

    <input type="hidden" name="products.Index" value="123" />
    <input type="text" name="products[123].Name" value="Chips" />
    <input type="text" name="products[123].Price" value="2.23" />

    <input type="submit" />
</form>

Post array looks a bit like:

products.Index=cold&products[cold].Name=Beer&products[cold].Price=7.32&products.Index=123&products[123].Name=Chips&products[123].Price=2.23

Model:

public class CreditorViewModel
{
    public CreditorViewModel()
    {
        this.Claims = new HashSet<CreditorClaimViewModel>();
    }
    [Key]
    public int CreditorId { get; set; }
    public string Comments { get; set; }
    public ICollection<CreditorClaimViewModel> Claims { get; set; }
    public CreditorClaimViewModel[] ClaimsArray { 
        get { return Claims.ToArray(); }
    }
}

public class CreditorClaimViewModel
{
    [Key]
    public int CreditorClaimId { get; set; }
    public string CreditorClaimType { get; set; }
    [DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:N2}")]
    public Decimal ClaimedTotalAmount { get; set; }
}

Controller GET:

public async Task<ActionResult> Edit(int id)
    {
        var testmodel = new CreditorViewModel
        {
            CreditorId = 1,
            Comments = "test",
            Claims = new HashSet<CreditorClaimViewModel>{
                new CreditorClaimViewModel{ CreditorClaimId=1, CreditorClaimType="1", ClaimedTotalAmount=0.00M},
                new CreditorClaimViewModel{ CreditorClaimId=2, CreditorClaimType="2", ClaimedTotalAmount=0.00M},
            }
        };
        return View(model);
    }

Edit.cshtml:

@Html.DisplayNameFor(m => m.Comments)
@Html.EditorFor(m => m.Comments)

<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(m => Model.Claims.FirstOrDefault().CreditorClaimType)
        </th>
        <th>
            @Html.DisplayNameFor(m => Model.Claims.FirstOrDefault().ClaimedTotalAmount)
        </th>
    </tr>        
<!--Option One-->
@foreach (var item in Model.Claims)
{
    var fieldPrefix = string.Format("{0}[{1}].", "Claims", item.CreditorClaimId);
    <tr>
        <td>
            @Html.DisplayFor(m => item.CreditorClaimType)
        </td>
        <td>
        @Html.TextBox(fieldPrefix + "ClaimedTotalAmount", item.ClaimedTotalAmount.ToString("F"),
        new
        {
            @class = "text-box single-line",
            data_val = "true",
            data_val_number = "The field ClaimedTotalAmount must be a number.",
            data_val_required = "The ClaimedTotalAmount field is required."
        })
        @Html.Hidden(name: "Claims.index", value: item.CreditorClaimId, htmlAttributes: null)
        @Html.Hidden(name: fieldPrefix + "CreditorClaimId", value: item.CreditorClaimId, htmlAttributes: null)
        </td>
    </tr>
    }
</table>    
<!--Option Two-->
@for (var itemCnt = 0; itemCnt < Model.ClaimsArray.Count(); itemCnt++)
{
    <tr>
        <td></td>
        <td>
            @Html.TextBoxFor(m => Model.ClaimsArray[itemCnt].ClaimedTotalAmount)
            @Html.HiddenFor(m => Model.ClaimsArray[itemCnt].CreditorClaimId)
    </td></tr>
}

Form is processed in the Controller:

Post Model:

public class CreditorPostViewModel
{
    public int CreditorId { get; set; }
    public string Comments { get; set; }
    public ICollection<CreditorClaimPostViewModel> Claims { get; set; }
    public CreditorClaimPostViewModel[] ClaimsArray  { get; set; }
}

public class CreditorClaimPostViewModel
{
    public int CreditorClaimId { get; set; }
    public Decimal ClaimedTotalAmount { get; set; }
}

Controller:

[HttpPost]
    public ActionResult Edit(int id, CreditorPostViewModel creditorVm)
    {
        //...