Django AutoSlugField across inherited models

Question

I'm wondering if you can have slugs unique across inherited models?

I have three models, one base and two that extend it.

The base has a unique AutoSlugField that is generated from the name field.

The slug is on the BaseModel however if I save a Hamster and an Elderberry both with the same name then I get an IntegrityError.

Clearly this is because the uniqueness is not enforced at the Base level but at the subclass level. Has anyone got a good solution for this?

BaseModel is not abstract and needs to stay that way as I'm using the 'django-model-utils' InheritanceManager.

setup

Django==1.4.3
django-extensions==1.0.2
django-autoslug==1.6.1

models.py

class BaseModel(models.Model):
    name = models.CharField(max_length=255)
    slug = AutoSlugField(populate_from='name', unique=True, db_index=True)
    # ... other fields

    objects = InheritanceManager()

class HamsterModel(BaseModel):
    useful_info = models.CharField(max_length=128)
    # ... other fields

class ElderberryModel(BaseModel):
    pointless_info = models.CharField(max_length=128)
    # ... other fields

console

>>> h = HamsterModel()
>>> h.name = 'One'
>>> h.save()
>>> h.slug
u'one'
>>> e = ElderberryModel()
>>> e.name = 'One'
>>> e.save()
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/blah/.envs/vfaces/local/lib/python2.7/site-packages/django/db/models/base.py", line 463, in save

    self.save_base(using=using, force_insert=force_insert, force_update=force_update)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/models/base.py", line 506, in save
_base
    self.save_base(cls=parent, origin=org, using=using)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/models/base.py", line 551, in save
_base
    result = manager._insert([self], fields=fields, return_id=update_pk, using=using, raw=raw)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/models/manager.py", line 203, in _
insert
    return insert_query(self.model, objs, fields, **kwargs)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/models/query.py", line 1593, in in
sert_query
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 912,
 in execute_sql
    cursor.execute(sql, params)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/backends/util.py", line 40, in exe
cute
    return self.cursor.execute(sql, params)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 114,
 in execute
    return self.cursor.execute(query, args)
  File "/home/blah/.envs/vfaces/local/lib/python2.7/site-packages/MySQLdb/cursors.py", line 201, in execute
    self.errorhandler(self, exc, value)
  File "/home/blah/.envs/blah/local/lib/python2.7/site-packages/MySQLdb/connections.py", line 36, in default
errorhandler
    raise errorclass, errorvalue
IntegrityError: (1062, "Duplicate entry 'one' for key 'slug'")

Answer 1

OK so after digging through the source code it turns out the docs have updated since I lasted looked.

So, if you add objects = models.Manager() to your BaseModel and pass that to the AutoSlugField. This will check the slug against BaseModel rather than the sub class.

class BaseModel(models.Model):
    objects = models.Manager()
    name = models.CharField(max_length=255)
    slug = AutoSlugField(populate_from='name', unique=True, db_index=True, managers=objects)
    # ... other fields

Answer 2

In database you have only one slug field in BaseModel table, HamsterModel and ElderberryModel are connected to BaseModel using foreign key. The only way I see in this situation is remove unique=True and check uniqueness at model level in save method.