def mongo_load(database, collection_key, id_key):
    """Load data from MongoDB database.

    Args:
        database (:class:`pymongo.database.Database`): MongoDB database to save
            results to.
        collection_key (str): name of collection.
        id_key (str): id key to look up data.

    Returns:
        retrieved data (returns None if no data with :attr:`id_key` is found).
    """
    return database[collection_key].find_one({'_id': id_key})
