class ManyRelatedObjectsDescriptor(object):
    # This class provides the functionality that makes the related-object
    # managers available as attributes on a model class, for fields that have
    # multiple "remote" values and have a ManyToManyField pointed at them by
    # some other model (rather than having a ManyToManyField themselves).
    # In the example "publication.article_set", the article_set attribute is a
    # ManyRelatedObjectsDescriptor instance.
    def __init__(self, related):
        self.related = related   # RelatedObject instance

    def __get__(self, instance, instance_type=None):
        if instance is None:
            raise AttributeError, "Manager must be accessed via instance"

        # Dynamically create a class that subclasses the related
        # model's default manager.
        rel_model = self.related.model
        superclass = rel_model._default_manager.__class__
        RelatedManager = create_many_related_manager(superclass)

        qn = connection.ops.quote_name
        manager = RelatedManager(
            model=rel_model,
            core_filters={'%s__pk' % self.related.field.name: instance._get_pk_val()},
            instance=instance,
            symmetrical=False,
            join_table=qn(self.related.field.m2m_db_table()),
            source_col_name=qn(self.related.field.m2m_reverse_name()),
            target_col_name=qn(self.related.field.m2m_column_name()),
            field_name=self.related.field.name
        )

        return manager

    def __set__(self, instance, value):
        if instance is None:
            raise AttributeError, "Manager must be accessed via instance"

        manager = self.__get__(instance)
        manager.clear()
        manager.add(*value)

class ReverseManyRelatedObjectsDescriptor(object):
    # This class provides the functionality that makes the related-object
    # managers available as attributes on a model class, for fields that have
    # multiple "remote" values and have a ManyToManyField defined in their
    # model (rather than having another model pointed *at* them).
    # In the example "article.publications", the publications attribute is a
    # ReverseManyRelatedObjectsDescriptor instance.
    def __init__(self, m2m_field):
        self.field = m2m_field

    def __get__(self, instance, instance_type=None):
        if instance is None:
            raise AttributeError, "Manager must be accessed via instance"

        # Dynamically create a class that subclasses the related
        # model's default manager.
        rel_model=self.field.rel.to
        superclass = rel_model._default_manager.__class__
        RelatedManager = create_many_related_manager(superclass)

        qn = connection.ops.quote_name
        manager = RelatedManager(
            model=rel_model,
            core_filters={'%s__pk' % self.field.related_query_name(): instance._get_pk_val()},
            instance=instance,
            symmetrical=(self.field.rel.symmetrical and instance.__class__ == rel_model),
            join_table=qn(self.field.m2m_db_table()),
            source_col_name=qn(self.field.m2m_column_name()),
            target_col_name=qn(self.field.m2m_reverse_name()),
            field_name=self.field.name
        )

        return manager

    def __set__(self, instance, value):
        if instance is None:
            raise AttributeError, "Manager must be accessed via instance"

        manager = self.__get__(instance)
        manager.clear()
        manager.add(*value)