clouds = Cloud.objects.filter(pk__in=pk_set)
    projects = structure_models.Project.objects.filter(pk__in=pk_set)
    if action == 'post_add':
        if reverse:
            for added_cloud in clouds.iterator():
                marry_cloud_to_project(added_cloud, instance)
        else:
            for added_project in projects.iterator():
                marry_cloud_to_project(instance, added_project)
    elif action == 'pre_remove':
        if reverse:
            for added_cloud in clouds.iterator():
                divorce_cloud_from_project(added_cloud, instance)
        else:
            for added_project in projects.iterator():
                divorce_cloud_from_project(instance, added_project)
    elif action == 'pre_clear':
        if reverse:
            for added_cloud in instance.clouds.iterator():
                divorce_cloud_from_project(added_cloud, instance)
        else:
            for added_project in instance.projects.iterator():
                divorce_cloud_from_project(instance, added_project)