django - update date automatically after a value change

Question

In the following django model:

class MyModel(models.Model):
    published = models.BooleanField(default=False)
    pub_date = models.DateTimeField('date published')

I want the pub_date field to be automatically updated with the current date, every time the published field changes to True.

What is the smart way?

Thanks.

Answer 1

You want to add the auto_now field and set it to True. This will update with the current timestamp each time you update the model.

pub_date = models.DateTimeField('date_published', auto_now=True)

You can read about it here

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Edit

Sorry you really just want to change the timestamp when the value of published is set to True. A really easy way to do this is to get the original value of the model and then override the save method so that it gets updated when it is set to True. Here is what you add to your code:

class MyModel(models.Model):
    published = models.BooleanField(default=False)
    pub_date = models.DateTimeField('date published')

    def __init__(self, *args, **kwargs):
        super(MyModel, self).__init__(*args, **kwargs)
        self._published = self.published

    def save(self, *args, **kwargs):
        if not self._published and self.published:
            self.pub_date = django.timezone.now()
        super(MyModel, self).save(*args, **kwargs)

Answer 2

All answers were useful, but I finally did it this way:

def save(self, *args, **kwargs):
    if self.published and self.pub_date is None:
        self.pub_date = timezone.now()
    elif not self.published and self.pub_date is not None:
        self.pub_date = None
    super(Model, self).save(*args, **kwargs)