@Override
    protected ObjectRelationMapper<UserModel> getObjectRelationMapper() {
        return userParentUserGroupMapper;
    }
Mapper for the relations between users and the user groups of which they
are members.
extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/user/UserParentUserGroupSet.java