Validation summary for a subset of fields

Question

I have a form that contains 3 distinct sections that looks something like this:

<form action="/Submit/" method="POST">
    <h2>
        Your Info:
    </h2>
    <ul>
        <li>
            <label>
                First Name:
                @Html.TextBoxFor(m => m.FirstName)
            </label>
        </li>
        <li>
            <label>
                Last Name:
                @Html.TextBoxFor(m => m.LastName)
            </label>
        </li>
    </ul>
    <h2>
        Membership:
    </h2>
    <ul>
        <li>
            <label>@Html.RadioButtonFor(m => m.MembershipLength_Months, 3) 3 Months</label>
        </li>
        <li>
            <label>@Html.RadioButtonFor(m => m.MembershipLength_Months, 12) 12 Months</label>
        </li>
    </ul>
   <h2>
        Billing Info:
    </h2>
    @Html.EditorFor(m=> m.PaymentInfo)
    <input type="submit" value="Submit" />
</form>

What I'd like to do is to have a summary per section. I know I could do something like this under each H2:

@if (ViewData.ModelState.Keys.Contains("FirstName") || ViewData.ModelState.Keys.Contains("LastName"))
{
    <div>
        summary text
        @Html.ValidationMessageFor(m => m.FirstName)
        @Html.ValidationMessageFor(m => m.LastName)
    </div>
}

But it feels like there should be a cleaner solution. Google has completely failed me and I haven't been able to find a custom helper or validation summary extension that takes a collection to represent the properties to summarize.

Each of the sections contains a good number of fields so the ModelState.Keys comparison gets pretty ugly pretty quickly. Is there a clean way to do this?

Answer 1

But it feels like there should be a cleaner solution.

Yes, you could write a custom, reusable HTML helper to achieve this task:

public static class HtmlExtensions
{
    public static IHtmlString Summary<TModel>(
        this HtmlHelper<TModel> html, 
        params Expression<Func<TModel, object>>[] expressions
    )
    {
        var div = new TagBuilder("div");
        var sb = new StringBuilder();
        foreach (var expression in expressions)
        {
            var unary = expression.Body as UnaryExpression;
            if (unary != null && unary.NodeType == ExpressionType.Convert)
            {
                var lambda = Expression.Lambda(unary.Operand, expression.Parameters);                    
                sb.AppendLine(html.ValidationMessage(ExpressionHelper.GetExpressionText(lambda)).ToHtmlString());
            }
            else
            {
                sb.AppendLine(html.ValidationMessageFor(expression).ToHtmlString());
            }
        }
        div.InnerHtml = sb.ToString();
        return new HtmlString(div.ToString());
    }
}

which could be used like that:

<h2>
    Your Info:
    @Html.Summary(
        x => x.FirstName,
        x => x.LastName
    )
</h2>

The helper allows you to list any properties you want to be included in the summary as validation errors.