from django.conf import settings

from django.db import models

from django.db.models.fields import FieldDoesNotExist

class CurrentSiteManager(models.Manager):

    "Use this to limit objects to those associated with the current site."

    def __init__(self, field_name='site'):

        super(CurrentSiteManager, self).__init__()

        self.__field_name = field_name

        self.__is_validated = False

    def get_query_set(self):

        if not self.__is_validated:

            try:

                self.model._meta.get_field(self.__field_name)

            except FieldDoesNotExist:

                raise ValueError("%s couldn't find a field named %s in %s." % \

                    (self.__class__.__name__, self.__field_name, self.model._meta.object_name))

            self.__is_validated = True

        return super(CurrentSiteManager, self).get_query_set().filter(**{self.__field_name + '__id__exact': settings.SITE_ID})