title: Initialize model object and check validity before saving to DB
body: <p>Is there any way to initialize a model object like:</p>
  
  <pre><code>@review = current_user.reviews.build(params[:review])
  </code></pre>
  
  <p>and then check it's validity against the validation rules in review.rb?</p>
  
  <p>...without attempting to save the model object to the DB??</p>