title: Raise a validation error in a model's save method in Django
body: <p>I'm not sure how to properly raise a validation error in a model's save method and send back a clear message to the user.</p>
  
  <p>Basically I want to know how each part of the "if" should end, the one where I want to raise the error
  and the one where it actually saves:</p>
  
  <pre><code>def save(self, *args, **kwargs):
      if not good_enough_to_be_saved:
          raise ValidationError
      else:
          super(Model, self).save(*args, **kwargs)
  </code></pre>
  
  <p>Then I want to know what to do to send a validation error that says exactly to the user what's wrong just like the one Django automatically returns if for example a value is not unique.
  I'm using a (ModelForm) and tune everything from the model.</p>