Connection() : pqxx::connection("dbname=hydra") { };

    Connection() : pqxx::connection(getFlags()) { };
    string getFlags()
    {
        string s = getEnv("HYDRA_DBI", "dbi:Pg:dbname=hydra;");
        string prefix = "dbi:Pg:";
        if (string(s, 0, prefix.size()) != prefix)
            throw Error("$HYDRA_DBI does not denote a PostgreSQL database");
        return concatStringsSep(" ", tokenizeString<Strings>(string(s, prefix.size()), ";"));
    }