# Hints, tips and tricks¶

Within a permission class, you can refer to the user and group using self:

class CampaignPermission(permissions.BasePermission):
label = 'campaign_permission'
checks = ('do_foo',)

def do_foo(self, campaign=None):
print self.user
print self.group
# ...


You can unregister permission classes and re-register them:

authority.unregister(Campaign)
authority.register(Campaign, CampaignPermission)


Within a permission class, you can refer to Django’s basic permissions:

class FlagpagePermisson(permissions.BasePermission):
label = 'flatpage_permission'
checks = ('do_foo',)

def do_foo(self, campaign=None):
if foo and self.change_flatpage():
# ...

authority.register(Flatpage, FlagpagePermisson)


If the Permission table changes during the lifespan of a django-authority permission instance and the smart cache is being used, you will need to call invalidate_permissions_cache in order to see that changes:

class UserPermission(permission.BasePermission):
label = 'user_permission'
checks = ('do_foo',)
authority.register(User, UserPermission)

user_permission = UserPermission(user)

# can_foo is False here since the permission has not yet been added.
can_foo = user_permission.has_user_perms('foo', user)

Permission.objects.create(
content_type=Permission.objects.get_content_type(User),
object_id=user.pk,
codename='foo',
user=user,
approved=True,
)

# can_foo is still False because the permission cache has not been
invalidated yet.
can_foo = user_permission.has_user_perms('foo', user)

user_permission.invalidate_permissions_cache()

# can_foo is now True
can_foo = user_permission.has_user_perms('foo', user)


This is particularly useful if you are using the permission instances during a request, where it is unlikely that the state of the Permission table will change.

Although the previous example was only passing in a user into the permission, smart caching is used when getting permissions in a group as well.