How can I use Django permissions without defining a content type or model?

I'd like to use a permissions based system to restrict certain actions within my Django application. These actions need not be related to a particular model (e.g. access to sections in the application, searching...), so I can't use the stock permissions framework directly, because the Permission model requires a reference to an installed content type.

I could write my own permission model but then I'd have to rewrite all the goodies included with the Django permissions, such as:

The possibility to assign permissions to users and groups.
The permission_required decorator.
User.has_perm and related user methods.
The perms template variable.
...

I've checked some apps like django-authority and django-guardian, but they seem to provide permissions even more coupled to the model system, by allowing per-object permissions.

Is there a way to reuse this framework without having defined any model (besides User and Group) for the project?

For those of you, who are still searching:

You can create an auxiliary model with no database table. That model can bring to your project any permission you need. There is no need to deal with ContentType or create Permission objects explicitly.

from django.db import models
        
class RightsSupport(models.Model):
            
    class Meta:
        
        managed = False  # No database table creation or deletion  \
                         # operations will be performed for this model. 
                
        default_permissions = () # disable "add", "change", "delete"
                                 # and "view" default permissions

        permissions = ( 
            ('customer_rights', 'Global customer rights'),  
            ('vendor_rights', 'Global vendor rights'), 
            ('any_rights', 'Global any rights'), 
        )

Right after manage.py makemigrations and manage.py migrate you can use these permissions like any other.

# Decorator

@permission_required('app.customer_rights')
def my_search_view(request):
    …

# Inside a view

def my_search_view(request):
    request.user.has_perm('app.customer_rights')

# In a template
# The currently logged-in user’s permissions are stored in the template variable {{ perms }}

{% if perms.app.customer_rights %}
    <p>You can do any customer stuff</p>
{% endif %}

Django's Permission model requires a ContentType instance.

I think one way around it is creating a dummy ContentType that isn't related to any model (the app_label and model fields can be set to any string value).

If you want it all clean and nice, you can create a Permission proxy model that handles all the ugly details of the dummy ContentType and creates "modelless" permission instances. You can also add a custom manager that filters out all Permission instances related to real models.

Following Gonzalo's advice, I used a proxy model and a custom manager to handle my "modelless" permissions with a dummy content type.

from django.db import models
from django.contrib.auth.models import Permission
from django.contrib.contenttypes.models import ContentType


class GlobalPermissionManager(models.Manager):
    def get_query_set(self):
        return super(GlobalPermissionManager, self).\
            get_query_set().filter(content_type__name='global_permission')


class GlobalPermission(Permission):
    """A global permission, not attached to a model"""

    objects = GlobalPermissionManager()

    class Meta:
        proxy = True

    def save(self, *args, **kwargs):
        ct, created = ContentType.objects.get_or_create(
            name="global_permission", app_label=self._meta.app_label
        )
        self.content_type = ct
        super(GlobalPermission, self).save(*args, **kwargs)

Fix for Chewie's answer in Django 1.8, which as been requested in a few comments.

It says in the release notes:

The name field of django.contrib.contenttypes.models.ContentType has been removed by a migration and replaced by a property. That means it’s not possible to query or filter a ContentType by this field any longer.

So it's the 'name' in reference in ContentType that the uses not in GlobalPermissions.

When I fix it I get the following:

from django.db import models
from django.contrib.auth.models import Permission
from django.contrib.contenttypes.models import ContentType


class GlobalPermissionManager(models.Manager):
    def get_queryset(self):
        return super(GlobalPermissionManager, self).\
            get_queryset().filter(content_type__model='global_permission')


class GlobalPermission(Permission):
    """A global permission, not attached to a model"""

    objects = GlobalPermissionManager()

    class Meta:
        proxy = True
        verbose_name = "global_permission"

    def save(self, *args, **kwargs):
        ct, created = ContentType.objects.get_or_create(
            model=self._meta.verbose_name, app_label=self._meta.app_label,
        )
        self.content_type = ct
        super(GlobalPermission, self).save(*args)

The GlobalPermissionManager class is unchanged but included for completeness.

How can I use Django permissions without defining a content type or model?

Related

Recent Posts