MVC 3 - Html.EditorFor seems to cache old values after $.ajax call

Question

This is a follow on from the following question:

MVC 3 + $.ajax - response seems to be caching output from partial view

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Answer 1

This was unexpected behavior for me, and although I understand the reason why it's necessary to give ModelState precedence, I needed a way to remove that entry so that the value from Model is used instead.

Here are a couple methods I came up with to assist with this. The RemoveStateFor method will take a ModelStateDictionary, a Model, and an expression for the desired property, and remove it.

HiddenForModel can be used in your View to create a hidden input field using only the value from the Model, by first removing its ModelState entry. (This could easily be expanded for the other helper extension methods).

/// 

/// Returns a hidden input field for the specified property. The corresponding value will first be removed from
/// the ModelState to ensure that the current Model value is shown.
/// 
public static MvcHtmlString HiddenForModel(this HtmlHelper helper,
    Expression> expression)
{
    RemoveStateFor(helper.ViewData.ModelState, helper.ViewData.Model, expression);
    return helper.HiddenFor(expression);
}

/// 

/// Removes the ModelState entry corresponding to the specified property on the model. Call this when changing
/// Model values on the server after a postback, to prevent ModelState entries from taking precedence.
/// 
public static void RemoveStateFor(this ModelStateDictionary modelState, TModel model,
    Expression> expression)
{
    var key = ExpressionHelper.GetExpressionText(expression);

    modelState.Remove(key);
}

Call from a controller like this:

ModelState.RemoveStateFor(model, m => m.MySubProperty.MySubValue);

or from a view like this:

@Html.HiddenForModel(m => m.MySubProperty.MySubValue)

It uses System.Web.Mvc.ExpressionHelper to get the name of the ModelState property. This is especially useful when you have "Nested" models since the key name isn't obvious.