def METHOD_NAME(self):
    """
    Get collection version from either version id, or from
    collection namespace, collection name, and version string.
    """
    version_pk = self.kwargs.get('version_pk', None)
    version_str = self.kwargs.get('version', None)
    if version_pk:
        return get_object_or_404(models.CollectionVersion, pk=version_pk)
    else:
        collection = self._get_collection()
        return get_object_or_404(
            models.CollectionVersion,
            collection=collection,
            version=version_str,
        )