def _reload_doc(cls, collection_name, sample_id, frame_number, hard=False):
        """Reloads the backing document for the given frame if it is in-memory."""
        if collection_name not in cls._instances:
            return

        frames = cls._instances[collection_name].get(str(sample_id), {})
        frame = frames.get(frame_number, None)
        if frame is not None:
            frame.reload(hard=hard)
Reloads the backing document for the given frame if it is in-memory.
fiftyone/core/singletons.py