@Override
    protected Integer mapPrimaryKey(ResultSet rs) throws SQLException {
        return rs.getInt("pets.id");
    }
{@link ResultSetExtractor} implementation by using the
{@link OneToManyResultSetExtractor} of Spring Data Core JDBC Extensions.
src/main/java/org/springframework/samples/petclinic/repository/jdbc/JdbcPetVisitExtractor.java