Django database generated slug

migration.py

"""Register a custom SLQ function to convert a string to a slug
https://gist.github.com/abn/779166b0c766ce67351c588489831852
This example is using Postgresql
"""
from django.db import migrations

SLUGIFY_FUNCTION = """
CREATE OR REPLACE FUNCTION public.slugify(
  v TEXT
) RETURNS TEXT
  LANGUAGE plpgsql
  STRICT IMMUTABLE AS
$function$
BEGIN
  -- 1. trim trailing and leading whitespaces from text
  -- 2. remove accents (diacritic signs) from a given text
  -- 3. lowercase unaccented text
  -- 4. replace non-alphanumeric (excluding hyphen, underscore) with a hyphen
  -- 5. trim leading and trailing hyphens
  RETURN trim(BOTH '-' FROM regexp_replace(lower(unaccent(trim(v))), '[^a-z0-9\\-_]+', '-', 'gi'));
END;
$function$;
"""


class Migration(migrations.Migration):

    dependencies = [
        ('balles_track', '0007_township_centroid'),
    ]

    operations = [
        migrations.RunSQL(SLUGIFY_FUNCTION)
    ]

models.py

class SlugifyFunc(Func):
  """Call for the custom function defined in the migration"""
  function = "SLUGIFY"

# Concat is not currently supported as Django 5.0 but should be in 5.1
# https://forum.djangoproject.com/t/using-generatedfield-with-postgres/27224
slugify_exp = ExpressionWrapper(
    SlugifyFunc(
        Concat(
            "departement",
            Value("-"),
            "commune",
            Value("-"),
            "date",
        ),
    ),
    output_field=models.SlugField()
)


# This does only works if the combination of brand, year and model is always unique
class Car(models.Model):
  brand = ...
  year = ...
  model = ...
  slug = models.GeneratedField(unique=True, expression=slugify_exp, db_persist=True, output_field=models.SlugField())