Generate unique slugs for Django models

generic.py

from django.template.defaultfilters import slugify

def generate_slug(cls, value):
    count = 1
    slug = slugify(value)
    if not isinstance(cls, type):
        cls = cls.__class__

    def _get_query(cls, **kwargs):
        if cls.objects.filter(**kwargs).count():
            return True

    while _get_query(cls, slug=slug):
        slug = slugify(u'{0}-{1}'.format(value, count))
        # make sure the slug is not too long
        while len(slug) > cls._meta.get_field('slug').max_length:
            value = value[:-1]
            slug = slugify(u'{0}-{1}'.format(value, count))
        count = count + 1
    return slug

specific.py

from django.template.defaultfilters import slugify

@classmethod
def generate_slug(self, name):
    count = 1
    slug = slugify(name)

    def _get_query(slug):
        if MyModel.objects.filter(slug=slug).count():
            return True

    while _get_query(slug):
        slug = slugify(u'{0}-{1}'.format(name, count))
        # make sure the slug is not too long
        while len(slug) > MyModel._meta.get_field('slug').max_length:
            name = name[:-1]
            slug = slugify(u'{0}-{1}'.format(name, count))
        count = count + 1
    return slug

Line 9 should be using exists() in both cases. There's not much difference in performance actually, but I think there would still be a small gain.