from django.db.models.fields import CharField


class SlugField(CharField):
    def __init__(self, *args, slugify=None, **kwargs):
        super().__init__(*args, **kwargs)
        self.slugify = slugify

    def pre_save(self, model_instance, add):
        if add:
            value = self.slugify(model_instance)
            setattr(model_instance, self.attname, value)
            return value
        return super().pre_save(model_instance=model_instance, add=add)