a postgres function to generate materialized path (ltree)

materialized_path_generator.sql

create or replace function create_path(parent_id_param bigint) returns ltree
    language plpgsql
as
$$
declare parent_path ltree;
    declare current_id BIGINT;
BEGIN
    SELECT currval('"comment_id_seq"') into current_id;

    IF parent_id_param is NOT NULL THEN
        SELECT path into parent_path FROM comment WHERE id = parent_id_param;
        return parent_path || current_id::text::ltree;
    end if;

    return current_id::text::ltree;
end;
$$;