Asp.Net MVC3 Razor - child items list not posting back from editor

Question

I'm trying to create a multi-level editor in MVC3. By multi-level I mean that I would like to be able to edit data for three levels of hierarchy (parent object, parent's child object and collection of sub-child objects). My model roughly looks like:

namespace MvcApplication1.Models
{
    public class Parent
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public Child Child { get; set; }
    }

    public class Child
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public IEnumerable<SubChild> SubChildren { get; set; }    
    }

    public class SubChild
    {
        public int Id { get; set; }
        public string Name { get; set; }
        private DateTime _date = DateTime.Now;
        public DateTime Date { get { return _date; } set { this._date = value; } }
    }
}

Since I want to display the whole hierarchy on one screen I created the following view model:

namespace MvcApplication1.Models.ViewModels
{
    public class ParentViewModel
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public Child Child { get; set; }
        public IEnumerable<SubChild> SubChildren { get { return Child.SubChildren; } set { this.Child.SubChildren = value; } }
    }
}

and controller is looks like:

    public class ParentController : Controller
    {
        public ActionResult MultiLevelEdit(int id)
        {
            // Simulate data retrieval 
            Parent parent = new Parent { Id = 2 , Name = "P"};
            var child = new Child { Id = 3, Name = "Cild1" };
            List<SubChild> children = new List<SubChild>();
            children.Add(new SubChild { Id = 3, Name = "S1"});
            children.Add(new SubChild { Id = 5, Name = "S 22" });
            child.SubChildren = children;
            parent.Child = child;
            // Create view model
            ParentViewModel vm = new ParentViewModel() { Id = parent.Id, Name = parent.Name, Child = parent.Child, SubChildren = parent.Child.SubChildren };

            return View(vm);
        }

    }

view being rendered is:

@model MvcApplication1.Models.ViewModels.ParentViewModel

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true)
    <fieldset>

    @Html.HiddenFor(model => model.Id)
    @Html.LabelFor(model => model.Name)
    @Html.EditorFor(model => model.Name)
    <hr />
    Child
    <br />
    @Html.EditorFor(model => model.Child)

    <hr />
    SubChild
    <br />
    @Html.EditorFor(model => model.SubChildren)


    <p>
            <input type="submit" value="Save" />
        </p>
    </fieldset>
}

I have created two editor templates in the Views\Shared\EditorTemplates :

ChildTemplate.cshtml

@model MvcApplication1.Models.Child

@{
    ViewBag.Title = "Child";
}

<h2>Child</h2>

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true)
    <fieldset>
        <legend>Child</legend>

        @Html.HiddenFor(model => model.Id)

        <div class="editor-label">
            @Html.LabelFor(model => model.Name, "Child Name")
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Name)
            @Html.ValidationMessageFor(model => model.Name)
        </div>
    </fieldset>
}

and SubChildTemplate.cshtml

@model MvcApplication1.Models.SubChild

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true)
    <fieldset>
        <legend>SubChild</legend>

        @Html.HiddenFor(model => model.Id)

        <div class="editor-label">
            @Html.LabelFor(model => model.Name)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Name)
            @Html.ValidationMessageFor(model => model.Name)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Date)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Date)
            @Html.ValidationMessageFor(model => model.Date)
        </div>
    </fieldset>
}

Everything renders correctly, however when I try to save the changes the SubChildren collection is null. I tried two signatures of the edit method:

[HttpPost]
public ActionResult MultiLevelEdit(ParentViewModel parentVM)
{...

[HttpPost]
public ActionResult MultiLevelEdit(ParentViewModel parentVM, FormCollection collection)
{...

and there is no value in any of those.

Can anyone suggest What could be improved to make that work? Thanks a lot in advance.

Answer 1

Your templates are not named correctly. Should be:

• ~/Views/Shared/EditorTemplates/Child.cshtml
• ~/Views/Shared/EditorTemplates/SubChild.cshtml

Also I don't quite see the purpose of the SubChildren property on your view model.

You could remove it and in your main view:

@model MvcApplication1.Models.ViewModels.ParentViewModel

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true)
    <fieldset>

    @Html.HiddenFor(model => model.Id)
    @Html.LabelFor(model => model.Name)
    @Html.EditorFor(model => model.Name)
    <hr />
    Child
    <br />
    @Html.EditorFor(model => model.Child)

    <hr />
    SubChild
    <br />
    @Html.EditorFor(model => model.Child.SubChildren)

    <p>
        <input type="submit" value="Save" />
    </p>
    </fieldset>
}

But your biggest problem is that you have nested HTML <form> elements which is not allowed. It's invalid HTML and results into undefined behavior. Some values might be posted, others not, ... Remove all Html.BeginForm helpers from inside your templates because your main view already contains a form.

Answer 2

See this article for a solution. The magic is contained in the using(Html.BeginCollectionItem("...")) block.

In short, you have to use the correct field names / prefixes when working with the default modelbinder.