Snippets Models

Model Related Snippets

Simple Permissions Model

class StandardPermission(models.Model):
    """
    An extremely basic base model for implementing object permission.
    The default implementation requires the model to have a user field
    (foreign key or onetoonefield) and allows permission if the user
    being checked either matches the user field or if the user being
    checked is a staff member.

    Extend the check_permission function as necessary to implement more
    elaborate functionality like group managers or multi-user accounts.

    Usage:
        good_user = User.objects.get(name='owner_user')
        bad_user = User.objects.get(name='random_account')

        object_with_permissions.check_permission(good_user)
        >>> True
        object_with_permissions.check_permission(bad_user)
        >>> False
    """
    class Meta:
        abstract = True

    _permission_type = 'standard'

    def check_permission(self, user):
        # your models need one of these fields
        # user = models.ForeignKey(User)
        # user = models.OneToOneField(User)
        return user.id == self.user.id or user.is_staff

Downcasting plain inherited models (use carefully, see docstring)

def naive_downcast(model_instance):
    """
    Downcasts a vanilla model instance. If not a subtype, returns the
    model_instance. CAUTION: Each test hits the database! Worst case will run
    a query for every subtype of the model class. If you need to use this often
    or on more than one instance at a time or on a model with lots of subclasses
    look into deeper options like
    https://github.com/carljm/django-model-utils#inheritancemanager.
    """

    # get app for model
    app_label = model_instance._meta.app_label

    # get other models from app
    app_models = models.get_models(models.get_app(app_label))

    # go through all the models
    for model in app_models:
        # if model is a subclass of the given instance's class
        if model_instance.__class__ in model._meta.parents:
            if hasattr(model_instance, model.__name__.lower()):
                # test database for this instance
                try:
                    return getattr(model_instance, model.__name__.lower())
                except ObjectDoesNotExist:
                    pass

    # didnt find anything, assume fully downcasted
    return model_instance

Downcasting inherited models that use django-model-utils inheritance manager

def inheritancemanager_downcast(model_instance):
    """
    Downcasts a model instance that is part of a model with objects
    set to inheritancemanager as defined in django-model-utils
    https://github.com/carljm/django-model-utils#inheritancemanager.
    """
    return model_instance.__class__.objects.get_subclass(id=model_instance.id)