Asp.net MVC3 Compare Attribute : Error when comparing against a nested property

Question

Getting an error when using MVC3 Compare attribute against a nested property.

Sample code is as follows:

Model and View Model :

public class Data
{
    public string Input { get; set; }
}

public class DataVM
{
    public Data Data { get; set; }
    [Compare("Data.Input")]
    public string ConfirmInput { get; set; }
}

Controller :

public ActionResult Data() {
    return View(new DataVM());
}

[HttpPost]
public ActionResult Data(FormCollection fc) {
    DataVM vm = new DataVM();
    TryUpdateModel(vm, fc);
    if (ModelState.IsValid){
        return Content("Success!!!");
    }
    return View(vm);
}

View:

@model myth.Models.ViewModels.DataVM

@using (Html.BeginForm()) {
@Html.ValidationSummary(true)

@Html.EditorFor(m => m.Data.Input)
@Html.ValidationMessageFor(m => m.Data.Input)
<br />
@Html.EditorFor(m => m.ConfirmInput)
@Html.ValidationMessageFor(m => m.ConfirmInput)
<br />
<input type="submit" value="Save" />
}
<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript">    </script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>

If I use [Compare("Input")], client side validation fails. If I use [Compare("Data.Input")], client side validation works but server side fails. In class CompareAttribute.cs, method

protected override ValidationResult IsValid(...) { .. }, 

fails to find Data.Input Property.

What is the correct way to use Compare for Nested Property comparison?

Answer 1

Change your view model and map back to your entity later:

public class DataVM
{
    public string Input { get; set; }

    [Compare("Input")]
    public string ConfirmInput { get; set; }
}