Retrieves the required resource.

def _get(cls, resource_id, parent_id, grandparent_id):
        """"Retrieves the required resource."""
        client = cls._get_client()
        endpoint = cls._endpoint.format(resource_id=resource_id or "",
                                        parent_id=parent_id or "",
                                        grandparent_id=grandparent_id or "")
        raw_data = client.get_resource(endpoint)
        raw_data["parentResourceID"] = parent_id
        raw_data["grandParentResourceID"] = grandparent_id
        return cls.from_raw_data(raw_data)