AutoSlugField

fields.py

from django.db import models
from slugify import slugify


class AutoSlugField(models.CharField):

    def __init__(self, populate_from, *args, always_update=False,
                 to_lower=False, max_length=50, **kwargs):
        self.populate_from = populate_from
        self.always_update = always_update
        self.to_lower = to_lower
        super().__init__(*args, max_length=max_length, **kwargs)

    def deconstruct(self):
        name, path, args, kwargs = super().deconstruct()
        kwargs['populate_from'] = self.populate_from
        if self.always_update:
            kwargs['always_update'] = self.always_update
        if self.to_lower:
            kwargs['to_lower'] = self.to_lower
        if self.max_length != 50:
            kwargs['max_length'] = self.max_length
        return name, path, args, kwargs

    def get_internal_type(self):
        return 'AutoSlugField'

    def pre_save(self, instance, add):
        value = self.value_from_object(instance)

        if self.always_update or not value:
            value = self.get_prepopulated_value(instance)

        slug = self.slugify(value)
        if self.unique:
            slug = self.generate_unique_slug(instance, slug)

        setattr(instance, self.name, slug)

        return slug

    def slugify(self, value):
        return slugify(value, to_lower=self.to_lower)

    def generate_unique_slug(self, instance, slug):
        new_slug = slug

        suffix = 2
        while (instance
               .__class__
               ._default_manager
               .filter(slug=new_slug)
               .exists()):
            new_slug = '{slug}-{suffix}'.format(slug=slug, suffix=suffix)
            suffix += 1

        return new_slug

    def get_prepopulated_value(self, instance):
        """
        Returns preliminary value based on `populate_from`.
        """
        if callable(self.populate_from):
            return self.populate_from(instance)
        else:
            attr = getattr(instance, self.populate_from)
            return callable(attr) and attr() or attr