Question

I’m using PRG for cleaning up my posts in MVC

On the POST action I store the controller modelstate in tempdata using an action filter and then redirect to the GET method which reloads the modelstate.

GET and POST action headers:

[ImportModelStateFromTempData]
public ActionResult Details(int id) { 
    var object = load(id);
    return View(object);
}

[HttpPost]
[ExportModelStateToTempData]
public ActionResult Details(MyViewModel model) { 
    update(model); return RedirectToAction("Details", new { id = model.id }) 
}

if an error occurs I in the post action I add an error to the modelstate which invalidates the modelstate and then redirect to the get action.

My question is how best can I determine, in the GET “Details” action that the model was in an error state after the post? If the modelstate was invalid I want to skip the logic…

var object = load(id);

in the GET action. I’ve tried ModelState.IsValid but this does not work.

Answer 1

You could try something like this:

public void OnActionExecuting(ActionExecutingContext filterContext)
{
    ModelStateDictionary modelState = filterContext.Controller.TempData[Key] as ModelStateDictionary;

    if( !modelState.IsValid )
    {
        filterContext.Controller.TempData.Add("IsValid", false);
    }
}

In your controller you can check the TempData[“IsValid”] field instead of ModelState.IsValid:

if( TempData["IsValid"] != null ) // do whatever here, or skip code etc.

Notice how the action filter code is in the OnActionExecuting method. YOu will keep the existing code in the OnActionExecuted:

public void OnActionExecuting(ActionExecutingContext filterContext)
{         ModelStateDictionary modelState = filterContext.Controller.TempData[Key] as ModelStateDictionary;

    if (modelState != null)
    {
        if (filterContext.Result is ViewResult)
        {
            filterContext.Controller.ViewData.ModelState.Merge(modelState);
        }
        else
        {
            filterContext.Controller.TempData.Remove(Key);
        }
    }
}