# Assign object permissions

Assigning object permissions should be very simple once permissions are created for models.

## Prepare permissions

Let’s assume we have following model:

    class Task(models.Model):
        summary = models.CharField(max_length=32)
        content = models.TextField()
        reported_by = models.ForeignKey(User, on_delete=models.CASCADE)
        created_at = models.DateTimeField(auto_now_add=True)

… and we want to be able to set custom permission assign_task. We let Django know to do so by adding `permissions` tuple to `Meta` class and our final model could look like:

    class Task(models.Model):
        summary = models.CharField(max_length=32)
        content = models.TextField()
        reported_by = models.ForeignKey(User, on_delete=models.CASCADE)
        created_at = models.DateTimeField(auto_now_add=True)

        class Meta:
            permissions = (
                ('assign_task', 'Assign task'),
            )

After we call management commands `makemigrations` and `migrate` our assign_task permission would be added to default set of permissions.

Note

By default, Django adds 4 permissions for each registered model:

- add_modelname

- change_modelname

- delete_modelname

- view_modelname

(where modelname is a simplified name of our model’s class). See https://docs.djangoproject.com/en/stable/topics/auth/default/#default-permissions for more detail.

There is nothing new here since creation of permissions is handled by django. Now we can move to assigning object permissions.

## Assign object permissions

We can assign permissions for any user/group and object pairs using same, convenient function: `guardian.shortcuts.assign_perm()`.

### For user

Continuing our example we now can allow Joe user to assign some task:

    >>> from django.contrib.auth.models import User
    >>> boss = User.objects.create(username='Big Boss')
    >>> joe = User.objects.create(username='joe')
    >>> task = Task.objects.create(summary='Some job', content='', reported_by=boss)
    >>> joe.has_perm('assign_task', task)
    False

Well, not so fast Joe, let us create an object permission finally:

    >>> from guardian.shortcuts import assign_perm
    >>> assign_perm('assign_task', joe, task)
    >>> joe.has_perm('assign_task', task)
    True

### For group

This case doesn’t really differ from user permissions assignment. The only difference is we have to pass `Group` instance rather than `User`.

    >>> from django.contrib.auth.models import Group
    >>> group = Group.objects.create(name='employees')
    >>> assign_perm('change_task', group, task)
    >>> joe.has_perm('change_task', task)
    False
    >>> # Well, joe is not yet within an *employees* group
    >>> joe.groups.add(group)
    >>> joe.has_perm('change_task', task)
    True

Another example:

    >>> from django.contrib.auth.models import User, Group
    >>> from guardian.shortcuts import assign_perm
    # fictional companies
    >>> company_a = Company.objects.create(name="Company A")
    >>> company_b = Company.objects.create(name="Company B")
    # create groups
    >>> company_user_group_a = Group.objects.create(name="Company User Group A")
    >>> company_user_group_b = Group.objects.create(name="Company User Group B")
    # assign object specific permissions to groups
    >>> assign_perm('change_company', company_user_group_a, company_a)
    >>> assign_perm('change_company', company_user_group_b, company_b)
    # create user and add it to one group for testing
    >>> user_a = User.objects.create(username="User A")
    >>> user_a.groups.add(company_user_group_a)
    >>> user_a.has_perm('change_company', company_a)
    True
    >>> user_a.has_perm('change_company', company_b)
    False
    >>> user_b = User.objects.create(username="User B")
    >>> user_b.groups.add(company_user_group_b)
    >>> user_b.has_perm('change_company', company_a)
    False
    >>> user_b.has_perm('change_company', company_b)
    True

## Assigning Permissions inside Signals

Note that the Anonymous User is created before the Permissions are created. This may result in Django signals, e.g. `post_save` being sent before the Permissions are created. You will need to take this into an account when processing the signal.

    @receiver(post_save, sender=User)
    def user_post_save(sender, **kwargs):
        """
        Create a Profile instance for all newly created User instances. We only
        run on user creation to avoid having to check for existence on each call
        to User.save.
        """
        user, created = kwargs["instance"], kwargs["created"]
        if created and user.username != settings.ANONYMOUS_USER_NAME:
            from profiles.models import Profile
            profile = Profile.objects.create(pk=user.pk, user=user, creator=user)
            assign_perm("change_user", user, user)
            assign_perm("change_profile", user, profile)

The check for `user.username != settings.ANONYMOUS_USER_NAME` is required otherwise the `assign_perm` calls will occur when the Anonymous User is created, however before there are any permissions available.