Asp.Net MVC: Fill a model property from a ActionFilterAttribute OnActionExecuting

Question

I'm implementing a captcha control for lost password in a website, like described here

But I feel very unconfortable with the `

filterContext.ActionParameters["captchaValid"] = recaptchaResponse.IsValid;

Because:

• I've a strongly typed view, with validators
• The day I will change the property name without remembering this string field, it won't works.

So I searched how to edit an attribute of my model in the ActionFilterAttribute, in the OnActionExecuting, because my controller action will need this data. I found this, but can't works for me since I need the model to be set BEFORE the action execute.

So I thought that I could add a "Post variable", which will be read by the model binder, but it seems that the filterContext.HttpContext.Request.Form is in read only mode.

So how do you think I could put the result in my model?

E.g: MyModel.IsCaptchaValid = recaptchaResponse.IsValid;

Event if I can't avoid to specify the property field, it's better than now:

filterContext.Something.Else["ModelKey"] = recaptchaResponse.IsValid;;

Answer 1

How about adding an error to ModelState e.g.

filterContext.Controller.ViewData.ModelState.AddModelError("", ""Captcha response invalid")

You can then check for ModelState.IsValid in your action (which you should be doing anyway)

Answer 2

The day I will change the property name without remembering this string field, it won't works.

If you are worried about a property / string name change breaking the functionality, you could unit test your custom attribute.

public void CaptchaValidatorAttribute_SetsActionParameter_ForCaptchaValidity()
{
    // arrange
    var filterContext = new ActionExecutingContext
    {
        ActionParameters = new Dictionary<string, object>()
        // ... other arrangements, like mocking HttpContextBase and HttpRequestBase
    };
    var actionFilter = new CaptchaValidatorAttribute();

    // act
    actionFilter.OnActionExecuting(filterContext);

    // assert
    Assert.AreEqual(filterContext.ActionParameters.ContainsKey("captchaValid"), 
        true);
}