title: Django: clean only specific model field?
body: <p>I have a Django model, something like:</p>
  
  <pre><code>class MyModel(models.Model):
     no_validation = models.PositiveIntegerField(null=True, db_index=True)
     yes_validation = models.CharField(max_length=254, validators=[my_validator])
  </code></pre>
  
  <p>I also have a pre-save hook that goes something like:</p>
  
  <pre><code>@receiver(pre_save, sender=MyModel)                                        
  def run_full_clean(sender, instance, **kwargs):                                 
     instance.clean_fields() 
  </code></pre>
  
  <p>My issue is that this current approach cleans all fields. I want to only clean one specific field (the one called yes_validation). Is there an easy way to do that?</p>
  
  <p>I'm only aware of the <code>exclude</code> parameter, but the issue is my class has almost a hundred different fields and so it would be a bit dirty to exclude every single one.</p>