How to check value transition in Django (django-admin)? (Revisited)

I was wondering about 开发者_运维百科how to control transitions in model data. I found the solution at How to check value transition in Django (django-admin)? but when I tried to implement it within my code, something went wrong (I am able to change the status with impunity):

Here is the relevant portion of my code:

# Blog Entry Draft Status Constants
ENTRY_STATUS_DRAFT = 0
ENTRY_STATUS_PUBLISHED = 1

# Create your models here.
class Blog(models.Model):
    title = models.CharField(max_length=200, unique=True)
    body_html = models.TextField(blank=True)
    pub_date = models.DateTimeField ('Date Published', blank=True, null=True, editable=False)
    PUB_STATUS = (
        (ENTRY_STATUS_DRAFT, 'Draft'),
        (ENTRY_STATUS_PUBLISHED, 'Published'),
    )
    status = models.IntegerField(choices=PUB_STATUS, default=0)

    def clean(self):
        # Don't allow draft entries to have a pub_date.
        if self.status == 'draft' and self.pub_date is not None:
            raise ValidationError('Draft entries may not have a publication date.')
        # Set the publication date for published items if it hasn't been set already
        if self.status == ENTRY_STATUS_PUBLISHED and not self.pub_date:
            self.pub_date = datetime.datetime.now()

    def clean_status(self):
        status = self.cleaned_data.get('status')
        if status == ENTRY_STATUS_DRAFT:
            if self.instance and self.instance.status == ENTRY_STATUS_PUBLISHED:
                raise ValidationError('You cannot change published to draft')
        return status

The clean() method works. I also tried using 'Published' and 'Draft' in the clean_status() method but that didn't work.

Am I putting clean_status in the right place? Am I overlooking something?

Your clean method should return the self.cleaned_data just like the clean_status returns the self.cleaned_data['status']. :)