Which is the best way to validate errors in Django?

Question

I found that there is a lot of ways to validate errors in Django, I'm just wondering which one is preferable and why?

e.g.

1. using clean in form, like:

       deadline = self.cleaned_data.get('deadline')
       if datetime.strptime(str(deadline)[:19], '%Y-%m-%d %H:%M:%S') < datetime.today():
           raise forms.ValidationError(_('Deadline cannot be in past!'))
       return deadline
   
   

2. before saving we can validate if there is any error and sending the instance if everything right, like:

    def save(self, force_insert=False, force_update=False, *args, **kwargs):
        if datetime.strptime(str(deadline)[:19], '%Y-%m-%d %H:%M:%S') < datetime.today():
            raise forms.ValidationError(_('Deadline cannot be in past!'))
        else:
            super(MODEL, self).save(force_insert, force_update, *args, **kwargs)
   

3. and not forgetting the validators in the model where I can use one in the filed it self like:

    deadline = models.DateTimeField(
                  verbose_name=_('deadline'),
                  validators=[MaxValueValidator(datetime.datetime.today())],
                  help_text=_('Note that the end time will be at the midnight of the day you picked.'),
   )
   

Also, we can do that in the forms in the class form we can check before saving if everything is right.

I want to know which is the best as a programmer and write a professional code.

Answer 1

In MVC, anything that touches the database should be in the model layer. You could have a method like 'is_valid_email(...)' on the User model and call that from your Form.

Note that the Model layer doesn't mean that you have to have a Class per table in your database VS creating new classes.

The Form is the Controller in DRF, I would go with option 1.