"""Ensures a unique slug field 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.
if getattr(item, slug_field): # if it's already got a slug, do nothing.
from django.template.defaultfilters import slugify
slug = slugify(getattr(item,slug_source))
itemModel = item.__class__
# the following gets all existing slug values
allSlugs = [sl.values() for sl in itemModel.objects.values(slug_field)]
if slug in allSlugs:
counterFinder = re.compile(r'-\d+$')
counter = 2
slug = "%s-%i" % (slug, counter)
while slug in allSlugs:
slug = re.sub(counterFinder,"-%i" % counter, slug)
counter += 1