Reserving primary keys in postgres using Ruby & Sequel

pg_array_to_int_array.rb

conxn    = Sequel.postgres(options)
pg_array = conxn["SELECT reserve_ids(#{table_name}, #{needed}) AS ids"].first[:ids]
new_ids  = pg_array.delete('{}').split(',').map(&:to_i)

reserve_ids.psql

CREATE OR REPLACE FUNCTION reserve_ids(table_name text, num integer)
RETURNS integer[] AS $body$
  DECLARE
    sequence_name text;
  BEGIN
    sequence_name = table_name || '_id_seq';
    RETURN array_agg(nextval(sequence_name)) FROM generate_series(1, num);
  END
$body$ LANGUAGE plpgsql;