python - Populating django field with pre_save()?

Question

class TodoList(models.Model):
    title = models.CharField(maxlength=100)
    slug = models.SlugField(maxlength=100)
    def save(self):
        self.slug = title
        super(TodoList, self).save()

I'm assuming the above is how to create and store a slug when a title is inserted into the table TodoList, if not, please correct me!

Anyhow, I've been looking into pre_save() as another way to do this, but can't figure out how it works. How do you do it with pre_save()?

is it like

def pre_save(self):
     self.slug = title

I'm guessing no. What is the code to do this?

Thanks!

Answer 1

Most likely you are referring to django's pre_save signal. You could setup something like this:

from django.db.models.signals import pre_save
from django.dispatch import receiver
from django.template.defaultfilters import slugify

@receiver(pre_save)
def my_callback(sender, instance, *args, **kwargs):
    instance.slug = slugify(instance.title)

If you dont include the sender argument in the decorator, like @receiver(pre_save, sender=MyModel), the callback will be called for all models.

You can put the code in any file that is parsed during the execution of your app, models.py is a good place for that.