What is the point of the key parameter in ModelState.AddModelError in ASP.NET MVC?

Question

I\'ve added validation checks in my controller that modify the ModelState if the validation fails.

For example:

Answer 1

The key parameter can be used to associate the validation error with a form field, and thus control where the message appears on-screen. It can be used with both HtmlHelper-type inputs and with simple HTML inputs.

If you've used @Html.TextBoxFor (or similar) and a @Html.ValidationMessageFor, you can get the key's value from the HTML name of the field being validated (use Inspect Element).

If you've just used an HTML , you can add a validation placeholder using @Html.ValidationMessage("AKeyIMadeUp"), and get a message to appear in it like this: ModelState.AddModelError("AKeyIMadeUp", "The value you entered is no good");.