title: ModelState.IsValid or Model.IsValid?
body: <p>I'm writing a controller and unit tests for it, when I came across two ways (equally valid I think) to do something.  All my models have an IsValid property, which I can check to ask the model if it's valid or not.  </p>
  
  <p>On postback to a controller action method, if the model is valid I want to save, otherwise I want to redisplay the form for the user to correct their errors.  </p>
  
  <p>My initial thought was to just verify that the model is being asked if it's valid, but I realized I could also check ModelState.IsValid.  </p>
  
  <p>Does anyone have any particular reason to look at one vs the other?</p>