asp.net Twitter Bootstrap TempData.Add(Alerts.Error error when adding two errors

Question

I'm using the twitter bootstrap nuget package for MVC.

When posting to my controller, and checking for errors however, if I have more than one error in my model, I get the following error when trying to add a second alert to TempData:

An item with the same key has already been added.

    //
    // POST: /Customer/Create
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create(Customer customer)
    {
        var errors = ModelState.Values.SelectMany(v => v.Errors);
        if (ModelState.IsValid)
        {
            // save to database etc
            // redirect to action
        }
        foreach (var c in errors)
        {
            TempData.Add(Alerts.ERROR, c.ErrorMessage);  // Error is reported here
        }

The error messages are difference, as shown below - so it must be that Alerts.ERROR is only allowed once:

Is there any way of adding two Alerts.Error error messages to TempData - or should I just concatenate a string, and add one error with combined error messages?

If I change the TempData code to:

TempData.Add(Alerts.ERROR, errors.Select(c => c.ErrorMessage).ToArray());

...the view renders as:

Thank you,

Mark

Answer 1

Why not just use TempData.Add(Alerts.ERROR, errors.Select(c => c.ErrorMessage).ToArray()) and iterate over the errors in your view?

Answer 2

TempData is a dictionary, so it makes sense that trying to add a duplicate key causes an exception. Depending on how you show the contents of TempData, you either want to concatenate the error messages into one string, or use a key that has a Guid appended to it (thereby making the key unique every time).

One possible workaround (within your loop):

if (TempData.ContainsKey(Alerts.ERROR))
{
    string temp = TempData[Alerts.ERROR].ToString();
    TempData[Alerts.ERROR] = string.Concat(temp, c.ErrorMessage);
}
else
{
    TempData.Add(Alerts.ERROR, c.ErrorMessage);
}

This naively assumes you've previously formatted your error messages, and will produce one long string. If you're using, say, a <ul> to display the errors, you would wrap each error message in a <li></li>, then concat.