If you want unique values for a slug field, but don't want to bother the user with error messages, this function can be put into a model's save function to automate unique slugs. It works by appending an integer counter to duplicate slugs.
The item's slug field is first prepopulated by slugify-ing the source field. If that value already exists, a counter is appended to the slug, and the counter incremented upward until the value is unique.
For instance, if you save an object titled Daily Roundup, and the slug daily-roundup is already taken, this function will try daily-roundup-2, daily-roundup-3, daily-roundup-4, etc, until a unique value is found.
Call from within a model's custom save() method like so:
`unique_slug(item, slug_source='field1', slug_field='field2')`
where the value of field slug_source will be used to prepopulate the value of slug_field.
Comments appreciated!
Watch out! Previous versions of this snippet (without the values list) were vulnerable to SQL injection attacks. The "correct" solution is probably to wait until [ticket 4102](http://code.djangoproject.com/ticket/4102) hits the trunk. But here's my temporary fix while we wait for that happy day.
Django's model.save() method is a PITA:
1. It does a SELECT first to see if the instance is already in the database.
2. It has additional database performance overhead because it writes all fields, not just the ones that have been changed.
3. It overwrites other model fields with data that may be out of date. This is a real problem in concurrent applications, like almost all web apps.
If you just want to update a field or two on a model instance which is already in the database, try this:
update_fields(user,
email='[email protected]',
is_staff=True,
last_login=datetime.now())
Or you can add it to your models (see below) and then do this:
user.update_fields(
email='[email protected]',
is_staff=True,
last_login=datetime.now())
To add it to your model, put it in a module called granular_update, then write this in your models.py:
import granular_update
class User(models.Model):
email = models.EmailField()
is_staff = models.BooleanField()
last_login = models.DateTimeField()
update_fields = granular_update.update_fields
I wanted to make the objects of a particular model approvable and store the timestamp of when that happened. In other frameworks/languages, I used to combined those in one "approved_at" field, which would be NULL if an object was currently unapproved.
I tried different approaches to implement this in django, and this is the best I came up with so far. Basically, the code in __setattr__ makes sure that the field, once set, will not be updated again.
Overriding setattr__() could also be a solution to determining if a field value has changed in save(), a question that seems come up from time to time in #django.