def remove_dataset_from_collection(dataset_id, collection_id, **kwargs):
    """
        Add a single dataset to a dataset collection.
    """
    collection_i = _get_collection(collection_id)
    collection_item = _get_collection_item(collection_id, dataset_id)
    if collection_item is None:
        raise HydraError("Dataset %s is not in collection %s.",
                                                    dataset_id,
                                                    collection_id)
    db.DBSession.delete(collection_item)
    db.DBSession.flush()

    db.DBSession.expunge_all()

    return 'OK'