def iter_chain(cur):
    """Iterate over all of the chains in the database.

    Args:
        cur (:class:`sqlite3.Cursor`):
            An sqlite3 cursor. This function is meant to be run within a :obj:`with` statement.

    Yields:
        list: The chain.

    """
    select = "SELECT nodes FROM chain"
    for nodes, in cur.execute(select):
        yield json.loads(nodes)