title: Before save model check some field
body: <p>I need to check if other models already created, have a field filled .
  If another model has the field with any value, the current model that attempts to create should not happen. And if possible send an error message.</p>
  
  <p>This is my current code:</p>
  
  <pre><code>class Video(models.Model):
    #####
    # Fields of model
    #####
  
    def save(self, force_insert=False, force_update=False, *args, **kwargs):
      some_video = Video.objects.all().filter(field_boolean=True).first()
      if not some_video:
        # Save current model
        super(Video, self).save(force_insert, force_update, *args, **kwargs)
      else:
        # avoid save method for the current model created and send error message
  </code></pre>
  
  <p>What am I doing wrong or what I'm missing? What is the correct way to do this?</p>