Django Multiple Databases But Auth In Single Db

Question

So I have a Django project with couple of databases:

default
login
foo
bar

Each app has it's own database (for example login app will store all models in login database etc).

I want to store all Django Admin related models such as permissions, users, groups in the default database. This is how my router looks:

class DBRouter(object):
    default_db_apps = (
        'auth',
        'admin',
        'contenttypes',
        'sessions',
    )

    def db_for_read(self, model, **hints):
        if model._meta.app_label in self.default_db_apps:
            return 'default'
        return model._meta.app_label

    def db_for_write(self, model, **hints):
        if model._meta.app_label in self.default_db_apps:
            return 'default'
        return model._meta.app_label

    def allow_relation(self, obj1, obj2, **hints):
            return True

    def allow_syncdb(self, db, model):
        if model._meta.app_label in self.default_db_apps:
            return db == 'default'
        return False

When I run:

python manage.py syncdb --noinput

It creates all auth related tables in the default database which is correct. When I look into auth_permissions table though, there are missing permissions for other apps. For example:

defaultdb=# select * from auth_permission;
 id |          name           | content_type_id |      codename      
----+-------------------------+-----------------+--------------------
  1 | Can add log entry       |               1 | add_logentry
  2 | Can change log entry    |               1 | change_logentry
  3 | Can delete log entry    |               1 | delete_logentry
  4 | Can add permission      |               2 | add_permission
  5 | Can change permission   |               2 | change_permission
  6 | Can delete permission   |               2 | delete_permission
  7 | Can add group           |               3 | add_group
  8 | Can change group        |               3 | change_group
  9 | Can delete group        |               3 | delete_group
 10 | Can add user            |               4 | add_user
 11 | Can change user         |               4 | change_user
 12 | Can delete user         |               4 | delete_user
 13 | Can add content type    |               5 | add_contenttype
 14 | Can change content type |               5 | change_contenttype
 15 | Can delete content type |               5 | delete_contenttype
 16 | Can add session         |               6 | add_session
 17 | Can change session      |               6 | change_session
 18 | Can delete session      |               6 | delete_session
(18 rows)

I would like permissions to all models (even models in different databases) to be stored in the default app.

Any solution for this?

Answer 1

The thing is that Permissions use foreign keys (generic foreign keys with ContentTypes if I remember well), and foreign keys between two databases are not supported!

See this post Django - multiple databases and auth.Permission

You can also read the limitation of multiple databases from Django documentation.

A few quotes:

Django doesn’t currently provide any support for foreign key or many-to-many relationships spanning multiple databases.

Several contrib apps include models, and some apps depend on others. Since cross-database relationships are impossible, this creates some restrictions on how you can split these models across databases:
- each one of contenttypes.ContentType, sessions.Session and sites.Site can be stored in any database, given a suitable router.
- auth models — User, Group and Permission — are linked together and linked to ContentType, so they must be stored in the same database as ContentType.