Question

I have a view with model BlogPostViewModel:

public class BlogPostViewModel
{
    public BlogPost BlogPost { get; set; }
    public PostComment NewComment { get; set; }
}

This view is rendered when action method BlogPost is hit. The view displays information regarding the blog post as well as a list of comments on the blog post by iterating over Model.BlogPost.PostComments. Below that I have a form allowing users to post a new comment. This form posts to a different action AddComment.

    [HttpPost]
    public ActionResult AddComment([Bind(Prefix = "NewComment")] PostComment postComment)
    {
        postComment.Body = Server.HtmlEncode(postComment.Body);
        postComment.PostedDate = DateTime.Now;
        postCommentRepo.AddPostComment(postComment);
        postCommentRepo.SaveChanges();
        return RedirectToAction("BlogPost", new { Id = postComment.PostID });
    }

My problem is with validation. How do I validate this form? The model of the view was actually BlogPostViewModel. I’m new to validation and am confused. The form uses the strongly-typed helpers to bind to the NewComment property of BlogPostViewModel and I included the validation helpers as well.

@using (Html.BeginForm("AddComment", "Blog")
{
    <div class="formTitle">Add Comment</div>
    <div>
        @Html.HiddenFor(x => x.NewComment.PostID) @* This property is populated in the action method for the page. *@
        <table>
            <tr>
                <td>
                    Name:
                </td>
                <td>
                    @Html.TextBoxFor(x => x.NewComment.Author)
                </td>
                <td>
                    @Html.ValidationMessageFor(x => x.NewComment.Author)
                </td>
            </tr>
            <tr>
                <td>
                    Email:
                </td>
                <td>
                    @Html.TextBoxFor(x => x.NewComment.Email)
                </td>
                <td>
                    @Html.ValidationMessageFor(x => x.NewComment.Email)
                </td>
            </tr>
            <tr>
                <td>
                    Website:
                </td>
                <td>
                    @Html.TextBoxFor(x => x.NewComment.Website)
                </td>
                <td>
                    @Html.ValidationMessageFor(x => x.NewComment.Website)
                </td>
            </tr>
            <tr>
                <td>
                    Body:
                </td>
                <td>
                    @Html.TextAreaFor(x => x.NewComment.Body)
                </td>
                <td>
                    @Html.ValidationMessageFor(x => x.NewComment.Body)
                </td>
            </tr>
            <tr>
                <td>
                </td>
                <td>
                    <input type="submit" value="Add Comment" />
                </td>
            </tr>
        </table>
    </div>
}

How in the AddComment action method do I implement validation? When I detect Model.IsValid == false then what? What do I return? This action method is only binding to the PostComment property of the pages initial BlogPostViewModel object because I don’t care about any other properties on that model.

Answer 1

You need to repopulate the model and send to view. However, you don’t need to do this by hand, you can use action filters.

see:

http://weblogs.asp.net/rashid/archive/2009/04/01/asp-net-mvc-best-practices-part-1.aspx#prg

Specifically:

public abstract class ModelStateTempDataTransfer : ActionFilterAttribute
{
    protected static readonly string Key = typeof(ModelStateTempDataTransfer).FullName;
}

public class ExportModelStateToTempData : ModelStateTempDataTransfer
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        //Only export when ModelState is not valid
        if (!filterContext.Controller.ViewData.ModelState.IsValid)
        {
            //Export if we are redirecting
            if ((filterContext.Result is RedirectResult) || (filterContext.Result is RedirectToRouteResult))
            {
                filterContext.Controller.TempData[Key] = filterContext.Controller.ViewData.ModelState;
            }
        }

        base.OnActionExecuted(filterContext);
    }
}

public class ImportModelStateFromTempData : ModelStateTempDataTransfer
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        ModelStateDictionary modelState = filterContext.Controller.TempData[Key] as ModelStateDictionary;

        if (modelState != null)
        {
            //Only Import if we are viewing
            if (filterContext.Result is ViewResult)
            {
                filterContext.Controller.ViewData.ModelState.Merge(modelState);
            }
            else
            {
                //Otherwise remove it.
                filterContext.Controller.TempData.Remove(Key);
            }
        }

        base.OnActionExecuted(filterContext);
    }
}

Usage:

[AcceptVerbs(HttpVerbs.Get), ImportModelStateFromTempData]
public ActionResult Index(YourModel stuff)
{
    return View();
}

[AcceptVerbs(HttpVerbs.Post), ExportModelStateToTempData]
public ActionResult Submit(YourModel stuff)
{
    if (ModelState.IsValid)
    {
        try
        {
            //save
        }
        catch (Exception e)
        {
            ModelState.AddModelError(ModelStateException, e);
        }
    }

    return RedirectToAction("Index");
}