title: Updating my model then re-evaluate IsValid?
body: <p>I'm passing in some values to my controller action and everything is binding up fine. There will be two properties missing from the form POST by design.</p>
  
  <p>I am then setting the missing values but then I want to validate the model and it is still saying false since it looks like the ModelState hasn't caught up with my changes.</p>
  
  <pre><code>[HttpPost, Authorize]
  public ActionResult Thread(int id, string groupSlug, Comment comment, string submitButton)
  {
    comment.UserID = UserService.UID;
    comment.IP = Request.UserHostAddress;
    UpdateModel(comment); //throws invalidoperationexception
    if (ModelState.IsValid) // returns false if i skip last line
    {
      //save and stuff
      //redirect
    }
    //return view
  }
  </code></pre>
  
  <p>What is the cleanest way to pat the ModelState on the head and tell it that everything will be okay whilst still validating everything else that was bound from the user's POST</p>